MAC11's I've seen around $5k. I've seen M16's for as cheap as $12k-14k. If I had 10k to drop on a full auto, I'd save another 4-5 and get a nice colt M16 from a motivated seller. Your lower receiver (the legal machine gun) can be built to have a billion uppers, caliber conversions, etc. Anything besides the lower receiver is just parts.