An Arduino, model bulldozer, servos, and sensors can be hacked together to make a sub-$100 robotics platform, appropriately named Ard-e.
While certainly nowhere near as fancy as this Wall-E replica, the price is right and the Arduino's got a huge body of pre-existing code for working with sensors that the aspiring roboticist can build upon. I'd particularly like to see a trash-compacting version...
Full disclosure: imadami is the maker of this project and also my youngest brother. And no, I don't want to hear about how much cooler this project is than my own!:)