Considering the postion at a border between two tribunals, could it be a suitable location for a RedCap inn ?
As a general rule, if you are low on goods/resources, try to provide service. In this case: trading outpost. Use magic to make the area safe by spotting threats and getting rid of them (or hiring/making a deal with them), some non-vis consuming spells can help clean the road (some basic form of ReTe Craft magic, requiring low Finess roll). If one is Merinita with access to Faerie magic and the "Road" duration/range, he can do some very useful stuff:
"As long as you walk on this Road, you won't be attacked by any bandits", ReCo road duration. You don't charge for this, but if the road is more secure, trade will be flourish.
If they decide to settle there, it means there is something valuable - can you elaborate ? If it is too miserable, why would they stay here ?
So they must have some form of valuable resources, otherwise just move away.
Is it a high Aura ? a rich source of virtus ?
If it is a high Aura, is there a Genius loci that they can befriend ? If you have thr Rhine Tribunal book, you would use the rule of forest spirit. I am sure that Transylvanian forest are wild and large enough to accomodate such characters.
Other option: there is a regio where life is comfortable and common resource (like fertile land and such) abudant. How do they secure access to this regio ? Can they convince people to go there and live ? preferable without this pesky priest who want to bring Dominion everywhere.
This is THE currency of the Order. They can hire a few mage specialists to cast the rituals they need to make life better, or order some items from Verdi. It is a common trade between the "wilder" tribunals (Novgorod mostly, but any large, wild area fits the bill) and the "more urbanised" tribunals (namely the Roman Tribunal).
There is no shame in using magic to help quick start a spring covenant in a wild location. In fact, yes, it is a common trope, but it is effective. Trading some virtus for a few casting tablets.
Rare library/text collection
First reaction: take it and move it somewhere more convenient !
Otherwise, it cannot be moved (maybe it is engraved in the wall of many caves). What prevent them from copying them over several seasons and move away ? Or if it is very valuable, can they seek sponsor from a Seeker, Bonisagus House (or Criamon or ...), a Mystery Cult which will provide them basic resources in return for maintaining the site and allowing access and residence for one of them two seasons a year ?
None of the above.
Err... Run away ?
Your question beg a few questions in return.
How big do your player want their covenant to be ? Do they want only them (no companion, no grogs), similar to the four magi estabished in Herisson Garden (Legends of Hermes). They will have to rely on several magic items for their daily chores, but they are mostly lesser enchanted item that could be purchased (or the lab text) for a low cost. In this case, they won't need much space and a cave with a heavy boulder that can only be moved by magic is a reasonable defense against most threats.
If they want to have several specialists, that's going to be a completely different story: how to convince them to come in the middle of nowhere ? How do you pay them ? Then you need to set up a steady source of income despite the apparent limited resource of the area.
The easiest is mentionned by Sanctaphrax: lumber trade.
The second one, with the help of a few InTe is the mining. Even without going to precious metal (which will attract all kind of bandits), basic stuff like coal and iron is a solid business. Volume are higher so transport need to be organise (and magic can help by shrinking cargo, reducing weight - to mention only lower magnitude spells).
If the issue is basic sustenance, but the magi have some silvers, the best is to stock up on foodstuff: large purchase in a city, shrink the whole think (MuHe, MuAn - if we use the Terram guideline Base is 4 for a 8 times volume reduction, so with touch +1, duration Moon +2, that's a level 20 - manageable, or 30 for a group of objets - manageable with a tablet, otherwise requiring a specialisation for a beginner magus, if the magus is travelling and does not mind casting it everyday, duration can be reduced to Sun - if casting is not possible lesser item can be purchased) to transport it more easily. According to Wikipedia, a mule can carry easily 70 kg, so before compression, that 560 kg. Enough to last for a long while. A healthy magus can easily travel with 20kg in his backpack, which is already quite a lot of food.
Then store it in a dry area (to prevent rot), possibly with a ward against vermin (ReAn 5 - can be spont cast)- the ward is not targetting the food so no side effect of warping food (again, it does not cost virtus). It is possible to have ward against rot, but it will target the foodstuff, so depending on the magnitude and duration of the storage, food can get warped (which can simply be a minor nuisance like unexpected taste). You resupply once or twice a year and you are good to go. If it is sustenance of a small group of people, it won't cost much.
If it is a whole turbula with dependants and relatives, you need a steady source of income, so refer to other suggestions.
I tried to present you only low cost/low magnitude options, that any magus out of apprenticeship should be able to pull off, with possibly the need for only lesser item or spell text. This kind of solution should not required owning major favor from a covenant, at most a minor favor from one magus (a season or two of work).
Building a whole covenant can be done "on the cheap", but it really depends on your take of Craft magic. There have been lengthy debates on this topic in this forum on what should be doable or not with Craft magic and how unbalancing/overpowering it can. Pick up your side as depending on the books you use, you will end up with different interpretations. I personally like it as it favors clever usage of spells and allows the "McGyver" style mage, but that's a personal taste.