As discussed in a recent thread, magic can significantly contribute to keeping a covenant's expenditures low (often a better idea than keeping the income high, because then you avoid the corrosive effects of inflation).
Now, Covenants states that "As a very simple rule of thumb, each magnitude of effect in [a work-saving enchanted device] can save one pound per year". Of course, immediately before that we find a more "precise" estimate of the potential savings for a specific device (a magical plough). So, in general, if one feels like doing the work of figuring out the actual savings, that should supercede the 1 pound/magnitude "rule of thumb".
Also, at the end of the same section, we read that "At the storyguide’s discretion, non-ritual Rego craft spells, if cast repeatedly over an extended period, may save money as per magic items." I would also assume that, by the same token, spells of other Techniques would also work -- I mean, creating wood or oil with D:Sun would be perfectly ok if the purpose was to burn them before the next sunrise/sunset. Of course, if these have to be cast repeatedly over the course of a season, with a handful of exceptions they either have to be invented as formulaics (which costs time), or to be cast as non-fatiguing magic.
This thread is about such non-fatiguing magic, ideally of the first magnitude or less (for which you need a casting score of 25, easily achievable even by a young magus with a little study). In general, D:Conc should be sufficient, as learning a single D:Sun/Moon formulaic version of Maintain the Demanding spell would allow all such magics to be sustained much longer. In addition to the spell, you should ideally provide a rough formula for the cost savings, based on the number of castings, size of the covenant, and lifestyle (beeswax candles are really expensive, so crafting them magically saves a lot of money compared to "real" candles, but not nearly as much if they substitude for the reeds a destitude covenant would employ).
I'll edit this post linking here every spell coming with a) the full level calculation (Base effect, RDT, etc.)
and b) some guess of the savings it can offer under different circumstances. So far we have:
The Gift of Athena, CrAq(He) 5, R:Touch, D:Sun, T:Ind, fills a barrel with olive oil
Ward against maggots, CrAn 5, R:Touch, D:Ring, T:Circle, preserves Animal foodstuff within
The Flaming Circle, CrIg 15, R:Touch, D:Ring, T:Ind, creates an enternally burning flame
The Invisible Groom, ReCo 4, R:Touch, D:Mom, T:Circle, cleans and grooms everyone in the circle