actually, an arduino+DS combination would work pretty well, as shown here:
http://www.youtube.com/watch?v=8sp8Is3Nuts
The arduino would be about $29.95, and about another $90 for the ds, a flashcard, a uSD card, and a protosheild for hooking up the robot stuff. The WPI library would have to be ported to the DS, and i don't know about a camera, but it should work, seeing that the DS has built-in wi-fi and all.