We use the local Tractor Supply for bulk animal feed. Buying in bulk can be a big cost up front, but saves a bunch in the long run. They also carry many pet, and as you would guess, farm related products. Decent store, friendly staff.

Plus they have a rewards program, so we basically get 50 lb of animal food free around every 3-4 months. Might be worth checking in with some local feed stores or even butcher shops for leavings and such.