Recently I've gotten into building robot kits with a friend. We built a little vibrating one that attempts to chase light, then we built one that drives itself around to avoid light. Both of these were kits. Next week we're building one that responds to sound. It goes forward until it hears a loud noise like a clap or whistle, stops reverses and turns, then continues forward. This is a kit as well. Next month we're going to attempt our first custom robot on a budget of $50. That price is including our board etc. I have a feeling it'll be made out of cardboard and CD's.