Meet the Makeblock mBot Ranger: a transformable STEM robot that works as a robot tank, three-wheeled racing car, and self-balancing 2 wheeled car. You can control these robots from your iPad or laptop using a visual programming interface.
The tank can handle a variety of terrains while the racing car can run and spin fast. This is based on an Arduino Mega 2560 with 5 on-board sensors and 10 extension ports. Costs under $190 at this time.