Gatling guns are legal if, as noted above, they are only operated by a hand crank. If the hand crank is powered by an electrical device, it becomes a machinegun, albeit an unregistered one. As I recall, the minigun used by Arnold in several movies was sold a few years ago by Stembridge for about $125k through LMO. The transferable last minigun I know of sold for about $275,000-$300,000 through Urban Armory, IIRC. FWIW, Brass Cartridge is working on (or maybe has completed) a .22 minigun with post-sample full auto models, and also hand cranked (non-NFA) versions. I think the hand cranked version runs about $10,000.
On a side note, two weeks ago I was a small machinegun shoot where one shooter brought a hand cranked Gatling gun. Absolutely beautiful - he had it made recently (at a cost of about $60,000), though I didn't ask who did the work.
