The Phenonstream is selling a tiny robot kit for $85, includes everything from motor, MCU, wheels, and building plates.
it looks quite solid to me. The SD card slot is actually an I2C interface to the Atmel AVRtiny84 host MCU, I am not sure how to program the AVRtiny84 with this SD card like PCB on your PC or Mac easily, may be more tutorials needed to be presented on its website. But anyway, if you are a hardcore engineer, you can just buy this kit and get the ISP pins out of it and program it yourself with your Atmel ISP programmer. Have fun!
Check out the kit: