I want to start a robotics project and need help?

I want to build a 4 wheeled or treaded robot capable of traveling over moderatly rough terrain. I want to start out making it RC, for testing purposes, then I want to add sensors and work with it being in full autonomus mode, but I still want to be able to go back to RC. I want a simple microcontroller capable of RC and autonomous modes that I can get for roughly $100 to $150. Any suggestions on great sites for robotics parts will also be apreciated.