Meet the Skeleton Bot Hercules: a 4WD mobile robotic platform that helps you get started in the world of robotics. It comes with an Arduino compatible board and has an open, expandable design. The kit consists of Hercules skeleton, motor controller, gear motor, and everything you need to get started.
Hercules is an open platform, so you can install additional components to customize your robot. Costs under $180 at this time.