There is no better way to teach STEM concepts than using robots, Arduinos, and electronics kits. Chip-E is an open source 3D printed robot with Arduino that you can build yourself. It is powered by RGS-13 servos, a RobotGeek Geekduino, and Sensor Shield components.
Chip-E has an open source design, so you can program it to do more or enhance it with your own custom 3D printed components. You get an IR gamepad to control the robot. Its 2×16 LCD display shows animations, patterns, and effects. This kit is available for under $150 at this time.