Let's Make Robots!

Basic platform - On the cheap

Hi, I'm planning to make a small set of self designed swarm bots.

 In terms of a mechanical platform, what's my best bet. My criteria are cheapness and easiness. Ideally, it should cost < $25 per platform, and be easy to make.

 So far, I'm thinking of pairing two solarbotics GM9 gearmotors and wheels with a thin wood base, and a third caster-esque wheel.

 Is this the best way to go?