Budget Robot - from avoider to follower and beyond
To the doubters* my 8 yo son and I say 'thbbbbbbsbb'. For about £30 we have an Arduino based 3 wheeled robot capable of object avoidance. We've since added a line following sensor and and a Bluetooth module.
*school 'friends' who said it couldn't be done and tried to dissuade my boy from his dreams.