This is a spinoff of my "Fi-dolla" line follower thread to detail how I'm hacking the D2-6 big brother of the cheap line follower into a cheap autonomous bot. This thread a bit premature since I just started today, but timely since it's on sale for a few more days at http://www.icstation.com/bluetooth-remote-control-smart-suite-tracking-kits-p-10171.html
It's still an everyday value at Banggood for $11.91: https://www.banggood.com/D2-6-DIY-51-MCU-Smart-Car-Kit-Bluetooth-Remote-Control-Gravity-Sensing-Tracing-Obstacle-Avoidance-p-1108390.html
IMO this may be a contender for the cheap merit badge robot we have discussed elsewhere. The stock robot has line following, obstacle detection and Bluetooth/smartphone remote control modes. The kit's 18-pin STC15W201S micro is easily replaced by your favorite processor since header pins are provided on the PCB chassis. There is a bit of SMT soldering on the stock kit. I'm no pro but I did a decent job and it all works. I'm adding a beeper and an IR remote receiver.
Attaching some pics. I'll add detail as the project progresses.