There is no better way to learn robotics and technology concepts than building and programming your own bots. Joop Brokking has shared a video that shows how you can build and program your own Arduino balancing robot. This robot uses stepper motors instead of DC motors. It takes about $80 to complete this.
You are going to need a Arduino pro mini/Uno, wireless motor, 2 stepper motors, a wired controller for Wii, 1 x 2200 mAh battery, and a few other parts to get started.