Mine are almost all from the grocery store. It took a while, but I found a chain store in an ethnic area that sells RMBs at great prices, plus I've started buying my own meat there as well. I find lamb ribs for $1.99 there, which is as low as they've been since I started in late 2001. Chicken leg quarters are frequently .59lb - and its very high quality meat! Whole Perdue chickens for between .89-.99lb

When you shop for meat & meaty bones, always consider quality before price. I used to get my leg quarters at a different store for .59lb, but they were old, low quality and always gave my dogs the runs. The meat I buy at the new store is good enough for me to eat myself.
As a side note, RMBs are the staple of a raw diet but please don't forget the muscle & organ meats - they're just as necessary and often left out too much in BARF style diets.