Cordless drill motors are great except that they pull a fair amount of current, shortening your run time. Call me cheap if you want but I scrounge the DC motors out of copy machines. They are usually 24 volt motors but they are 7 pole ball bearing motors, nice stuff. Now for the kicker, I unwind the armatures and rewind them with a larger size magnet wire for use at a lower voltage. The other nice thing about copy machines are that they are full of toothed belts and pulleys.

motor- free
wire- 50 cents