I'm thinking that pretty much ANY motor would work given the amount of torque increase provided by gear reduction. Even a weak motor capable of 10 oz-in of torque would have over 52 ft-lbs of torque when geared 1000:1.
Other options: vacuum cleaner motor (either the main motor or the spinning brushes motor), overhead bathroom fan (can get these for ~$15 at a home improvement center), drill motor (would have some gear reduction built in), etc. Out of these, a cheap drill might be the best bet for cost and the gearing built-in. Might be able to get away with "only" 500:1 gearing.
EDIT: Just checked
Harbor Freight and a simple 3/8" corded drill is $20.