Good question. Typically, raw is not as cheap as it was few years ago. Couple tips:
1. If you have a local butcher get the know them and arrange to buy the scraps and bones.
2. Look for the sale items in the supermarket - usually with yellow or red label. These are items that are about to expire and need to be sold. ground beef, ground turkey, Beef, chicken, turnkey necks, chicken backs etc.. but basically whatever uncooked meat that you can find. Bone in is best.
3. Supplement with an egg, greens (veggies) and probiotics (yogurt or cottage cheese)
Best wished and let us know how it goes.