A classic:
The Gift of Athena, CrAq(He) 5, R:Touch, D:Sun, T:Ind
Fills a large barrel with pure olive oil, that lasts until the next sunrise/sunset. Can be used for illumination, heating, hygiene, and cooking (it provides no nourishment, but it's great for frying). A variant with D:Moon requires less frequent attention by a magus but is second magnitude. A variant with D:Conc (to be combined with Maintain the Demanding Spell) would be only level 4.
Base 2 (Fill a container with a natural liquid (with appropriate requisites)), +1 Touch, +2 Sun
How much is this worth in savings? Hmm. First of all, it's a lot of fuel. If cast twice a day, it can probably suffice for a smallish covenant; half-a-dozen castings are probably sufficient for all but the largest covenants. But... how much? I'd eyeball it at maybe ... 1-10% of the provisions costs, with the higher range for covenants in cold climates. Let's be conservative and say 1 pound/year per 100 points of inhabitants, up to double that for covenants exposed to significant cold weather (windy mountaintops, the far north etc.). This automatically includes the fact that people living more luxuriously (i.e. costing more points of inhabitants) keep themselves better warmed etc. Obviously, this is not cumulative, or only partially cumulative, with other magics that create substances with similar purposes, e.g. wooden logs.