You have to look at each of the categories of expenses and think about how you could reduce them. While creating silver with a ritual can pay for all of them, it causes inflation and can draw the ire of the Order so is something that really should only be done in extreme moderation. Many Tribunals have measures restricting the wealth creation magic of all Covenants to 2 pounds of silver per magus per year (HoH:TL, p.87).
So what are the categories that we can cover? Buildings, Consumables, Provisions, and Wages are the big four for cost though we will ignore Wages since covering it involves wealth creation. Weapons & Armor, Laboratories, and Writing Materials are the smaller. Outside of strange circumstances we want to focus on the first three, which each individually tend to be larger than all of the smaller combined.
Buildings Expense
This expense covers maintenance, decoration, and furnishing of the Covenants buildings and is 10% of Inhabitants plus Fortification Boons cost. It also has a very high limit of 50% per Craft which means it can be offset by just focusing on two types. This is generally the cheapest of the big four So what can we do to reduce this cost?
Maintenance is the easiest. Sure you could try to directly replace craftsmen, but most of those items require finesse. You are better served by non-finesse items which improve the efficiency of craftsmen or reduce waste. An example is an item with a variation of 'Rock of Viscid Clay' effect which does both of those. It lets the craftsmen easily fix damage and allows them to use scrap rock as filler. You can do similar things with other Forms to cover different building materials.
Another way to reduce cost is something that helps produce raw materials. If you have a lot of wooden buildings (or even partially wooden) then an item that causes plants to grow to maturity rapidly can offset a portion of your cost. Items that provide finishing on raw materials such as speeding up the dressing of stone or seasoning of wood also help here.
Another type of item that is useful are Intellego effects which can be used to judge the quality/condition of buildings and material. Allowing your craftsmen to know when something needs to be repaired/replaced before it can normally be determined or if a set of replacement material is good is a valid way of cutting cost.
Actually producing glass from raw materials is more difficult and requires a Finesse roll, but you can target a low quality if you have an effect that does the actual shaping. Effects which turn glass to liquid for a short time can be used to create windows easily, including using scraps from broken ones. Covenants with access to quartz can use it as a replacement for glass with a similar "change to liquid" effect. It is also far easier to make stained glass when you do not have to melt it.
Something I don't think most consider is that illusion magic can serve as an effective way of providing decoration which does not deteriorate. Not something that most SG will allow a massive amount of savings from, but for larger Covenants even a max of 10% of the Building can be north of 10 pounds per year.
For Covenants with docks, you can create items which have a PeTe effect to destroy sentiment the clearing of which was a major expense. There is a cannon example of this as a rod that destroys dirt.
Consumable Expense
This expense is 20% of the Inhabitants and has a lower limit of 20% per Craft. So while it requires a wider range of items to fully offset it covers such a broad range that it is not very difficult. This category is mostly made up of items that are destroyed by use, even if that destruction can take a long time (clothing and wagon wheels).
Magical lights are the easiest saving here and most likely the most common in the Order. Enchanted lamps are cheap at 9 levels and 1 pawn each, with a given Magus often able to create several a season with lab text. Each of those is a 1.8 pound savings per year (up to that 20% limit). You could do larger enchantments for things like whole buildings.
Magical heat is another area. This does not just cover keeping warm but also things like cooking and supplying forges. So ovens and forges that produce their own heat reduce this. An enchanted item that creates Moon duration firewood is another good example.
Some of the items that reduced Building cost can be used here as well. Repairs of things like wagons are part of this expense so if you have items that can help with wood or metal (cooper, carpenter or tinker) then you can use them to save some money here.
Items which improve the quality or help repair clothing are another possibility. My Covenant uses presses which change cloth to a mud like consistency for a round. This can be used to repair tears and makes the cloth a monolithic material which is more resistant to damage.
Provisions Expense
This is the big one at 50% of the Inhabitants (plus larger animals) and uses the lower limit of 20% per Craft (plus 50% from Laborers). While the examples in Covenants only list two craftsmen to offset it (brewer and vintner), anything that helps produce or preserve food or drink is a valid choice.
Preserving items are a fairly easy choice. While you could do things like wards to keep out vermin or enchantments to protect against rot (TtA, p.93 has two such), there are other methods. Covenants has a CrAn and CrHe Base 2 (p.50 and p.51) which prevent animal bodies and dead plants from decaying. You can also use enchantments which cause an area to be cold or freezing, which can not only serve like a modern refrigerator or freezer but allow the actual production of ice. Just making an area cold is also beneficial to dry aging meat products (whole or things like sausages).
Providing clean water for drinking and cooking can also be useful, especially for Covenants located in areas with not much water. Access to potable water was a serious issue through much of human history. So enchanted items which move or clean water can be a valid means of cost savings. Movement is fairly easy with a range of ReAq options, but cleaning is often more difficult. For Covenants with access to lots of salt water, PeAq effects can be used to destroy the saltiness. MuAq effects can be used which separate the water into clean and contaminated portions. You could even build a large layered filter and use ReAq to move water into it.
For your more adult beverages you have many options. Rough processing of the ingredients (crushing grapes, milling grain), motion that animates the stirring of vats or makes rotating barrels easier, separation of the liquid from solids, and effects which increase the rate of fermentation (directly or indirectly) can all be used. You could even get way out there and introduce a magic still, allowing large scale production of distilled spirits a few centuries before it became common (the technology was already around for nearly half a millennia for small scale distilled alcohol production).
Anything that helps your plants grow rapidly is a possible "cost saving". Items can cause all plants in a green house to grown well or not become sick. For plants with an annual harvest you can use effects that cause them to blossom out of season which can greatly increase your total yield. An item that brings trees to maturity rapidly can be used to create massive fruit and nut orchards in very little time. Water movement effects are useful for irrigation. Wards can be used to keep out pest. You can produce effects which till the land. Items which allow controlling bees can also be useful.
For animals anything which allows controlling them can make herding easier and so serve as a cost savings. For those hunting/fishing, effects can be used to replace the need for bait. Illusions are the easiest and have a few cannon examples.
EDIT: There are many food animals which are classified as Vermin. If you have access to the appropriate matter that they generate from, then you can use the ReAn Base 5 (A&A, p.30) to spontaneously generate them from that matter. You could also use Creo Moon duration effects to create the matter, even better if it has a Constant effect so that it generates automatically twice a day. You could use these items to boost up a pound to produce a massive amount of vermin which could both be consumed and would boost the population of fish due to the abundance of food.
General Effects (and the smaller expenses)
For Laboratory expenses you generally want craftsmen. Skilled craftsmen can allow you to get the Superior Equipment and Superior Tools Lab Virtues for free, which will often be a larger reduction in total cost and boost in effectiveness than what you will get from any Covenant enchanted items. Any effect which helps with glass or metal can be used though normally it is better to put it towards one of the more expensive expenses.
Weapons & Armor and Writing Materials fall into much the same problem. They are generally low and can be offset by a couple of craftsmen without any enchanted items, with enchanted items often producing better results put to one of the larger expenses. They are both generally better served by a couple of craftsmen each which can generally cover all of their cost. However if you do have a massive military force you might consider a couple of items for Weapons & Armor which can also be used in other categories. For Writing Materials it is almost never worth it to devote cost saving enchanted items for Covenant use since a pair of even mid tier craftsmen (skill 4 or 5) can offset all of it and they are a type that cannot be readily used in other categories. Save those for improving Income Sources.
There are some effects which can easily jump between the varies Expenses. Things like self motive wheels can be used to power mills which could fall into any of the three. Grain mills for Provisions, lumber for Building and Consumables. They could even power things like bellows and whetstones which would allow them to be used for cost savings in Weapons & Armor or Laboratory Expenses.
Bonus
Another thing to take into account is how effective an enchanted item/ritual is for increasing a Source of Income is not really covered in the rules. It is something that individual SG need to decide upon so you can often get a better "bang for buck" (Cov, p.57, last paragraph). An item that might only be a cost savings of 5 pounds per year could provide up to a 50% permanent increase to an Income Source. Granted that is an extreme example and more likely to be in the 5~20% range.
Looking at things more realistically, should you take a 5 pound cost savings or a 5% increase in an Income Source? The Income Source of course, because all increases compound. It adds up fairly quickly. Taking five 5 pound cost savings is only 25 pounds total, while taking five 5% increases is over 27.6%. Additionally that 27.6% can increase further every year and any additional increases compound it.
Do not focus all of your efforts on increasing Sources of Income, since they are subject to chance and outer influences far more than Cost Savings. Compare to investing, with SoI being 'high risk' and CS being 'low risk'. You want a mix to get the most you can without over exposing yourself. How risky an individual group wants to be is up to them but generally a balanced approach will give the most consistent results.
) can be used by craftsmen, who will use their craft ability instead of Finesse. It can speed up the process, but as long as you are reasonable, the penalty on the crafting roll will remains manageable for standard quality items.