Actually, a good dedicated bolt gun for the big .50 will run at least 3-4K. The upper conversion costs about 2K for the Safety Harbor--at least the one I want.
I plan to get the LONG (29") barrel, to get all I can out of the cartridge.
As far as the recoil, the rep I talked to on the phone (from Safety Harbor) specifically said that there have been no issues with the mating or durability of the mounting on AR receivers. I plan to buy a dedicated receiver for it, too--along with possibly a Rock River 2 stage trigger, and a Magpul PRS stock.
And, I'm sure that with the brake mounted, the recoil can't be worse than my Sharps rifle (.45-120-550). At least, I hope not!