Ultimately, I would just get whole animals and dump it in the backyard for my dogs. Unfortunately, neither moderate their eating so would end up as bloated masses if I was to do this, so I have to portion up whole animals.
But I do things on the cheap. I buy any meats on sale for less than $4 a kilo. Chicken wings, necks, livers, drumsticks. Turkey drumsticks, necks. Lamb necks, 'offcuts', hearts, livers, kidneys. Beef liver. Pig hooves. These are some of the things I have bought.

The only thing NOT to feed is the femurs of large animals - e.g. cow femurs, as these bones are stronger than dog teeth and can shatter the dog's teeth.
So far I have mostly got stuff from the supermarket, but the pet shop near by has some items (mostly meaty bones) for a fair price, and I am going to try the butcher nearby as I have seen him advertising specials which beat the supermarket.

But my boyfriend has laid down the law - no more meat in the freezer until it's cleared out! ... I'm vegetarian too, so all the meat in our freezer is dog food!