This CNC milling machine costs a little under $1,000 and uses a drill head to carve out 3D objects in solid plastic. The iModela is made by Roland DG (a subsidiary of the guys who make musical instruments) and has a very Japanese UI and aesthetic, which is pretty cool. They offer some interesting free models and a plastic sample kit for folks interested in getting started.
Some BoingBoing commenters are also recommending the DeepGoove1 CNC mill that can mill steel as well as wood and plastic. These things might not be quite ready for general home use yet, but the fact that you can grab a CNC machine for around a grand is pretty incredible in itself.