How big? You could make it out of hacked servos and simple wheels and tires, and use a evelon mixer (think that's the name) to make a 2 ch pistol radio do the throttle and steering. For anything bigger, hit www.robotcombat.com for cheap motors. If you want even cheaper and 550 and smaller motors, www.allelectronics.com has some sweet stuff, including the famous $3.50 Johnson 550.