Here is another fun DIY idea for Portal fans. This Animatronic Wheatley from lukealbertson96 was built with 3D printed parts. It can move its face in all directions and tilt it side to side. You also get independent upper/lower eyelid function. 40+ voice lines are built-in.
You are going to need an Arduino Uno R3, micro servos, PS3 controller, amplified speakers, and a bunch of other components to pull this off. The total cost according to the maker is about $1800.