Try a 12V Window Crank Motor. Inexpensive, low current readily available.
http://www.princessauto.com/pal/product/8366478/
Or
Motor
Edit: the ones I use, form PA, draw 800ma at 5VDC (~17RPM) and 1amp at 9VDC (~25RPM)
The shaft is 1/2", and for what it's worth I cannot stall the motor with 4" pliers.