Confused about Unit Upkeep/Cost

A unit's upkeep cost is 10% of its price per season. Assuming a season is ~90 days, an example d6 infantry unit that costs 220 gp has an upkeep of 0.24 gp/day. This doesn't seem like enough to feed a unit of any size, let alone equip and train them.

Am I missing something about the cost and upkeep of units?