I think one of the cheapeast ways (if you have the time/space) is to raise your own poultry and or rabbits. I always buy a big batch of chicks every spring, feed all the roos to the dogs... roosters are easy to come by many times free. A month or so after Easter rabbits are plentiful and usually cheap. Next is to source locally as much as possible local butchers, poultry plants, fish mongers.