Like above, their ain’t no such thing as a cheap (legal) full-auto, But if you got the cash there are plenty of choices.
22lr
American 180 – $9k with 275 round drum
Uzi with 22-conversion kit – $8k+
M16 with 22 conversion kit – $9k-$20k
There are a few others, but these are the most common. I better bet would be to get an M11/9mm ($3k). Put a slow-fire setup on it and shoot till your ammo dries up! I have heard about a 22 conversion for these also, but most folks seem to have a lot of trouble with them. M16 is even better but will cost you 3-4 times as much. Lots of accessories and lots of fun if you can afford it.
Monkeybear – although there are a handful of transferable 10/22 machine guns out there, in this country you cannot make any more (since may 86) unless you go through tons of paperwork, make it for demonstration purposes for military/police, pay lots of money for taxes, business licenses, etc. Manufacturing a full auto for personal use anytime after the 86 cutoff equals prison.
Rangerruck – I think what you are referring to is the Calico Gatling gun setup. It is a kit that you put together using two Ruger 10/22 and fire by cranking a handle. These are not true machine guns, they are Gatling guns, but fire pretty quick all the same. Search online for a bit and you will find them; I’m pretty sure they are still being made. Never mind, just go here:
gatlingguns.com