So I'm still poking away at mercenary bands and similar armed groups and the expenses involved, which has ultimately brought me to the races like goblins and ogres for whom money isn't of any real value, but consistent good food, warm fires and well made bedrolls are.
So I was looking at the costs of alcohol and spices and things to pay for military service with basic comforts. Couldn't find drugs on any kind.
Ale is pretty cheap, a 40 gallon barrel is 2.8 gold, and 2 gold of that is the barrel. Common wine works out about the same.
Then I looked at saffron, it's 15 gold for a pound. Doesn't tell me much, so I need to know how much saffron you actually need when cooking. A 'pinch' does about 4-6 servings of stew or soup, ok, better, but how much is a pinch? Turns out it's twenty threads. How much does a thread weigh? Anyway long story short, that pound of saffron is enough to season 68000 servings of food. Throw in ginger, cinnamon, pepper, cloves and salt as things you can buy and keeping tasty food on the table seems easy if you can access a half decent field cook.
A chicken is just 2cp and should give about 3 pounds of meat, a goat is 1gp for about 40 pounds, a cow is 10gp for about 430 pounds, so meat isn't too expensive. Flour is cheap at 2cp a pound.
If you find soldiers that will work for bed, board and luxuries it seems quite practical to keep them happy for months or even years with pretty low expenses. I'm sure more than a few ogres and hill giants would be willing to work for all the delicious meat stew and spiced bread they can eat, all the ale they can drink and a soft warm place to sleep. The inevitable brawls would be an issue, but plenty of races in D&D get them to work for them without much issue and they just pay them in raw meat, beatings and the occasional captive to torment.
Finding enough work for them to earn their keep is probably the hardest part of maintaining a band of soldiers, but hey, most D&D settings are rife with problems that can be solved by violence.