2WD Robot Platform, $50
Do you already have an Arduino (or other microcontroller) and sensor components and want to turn them into an autonomous robot? Our robot platform includes a sturdy aluminum chassis, 2 gearmotors, 2 wide plastic wheels, an omnidirectional 3rd wheel, and all of the hardware for assembly. Just add senses and a brain!
Also available as a 4WD platform, with all of the above parts plus two more gearmotors and wheels and a rectangular platform.