As discussed on a thread in the hardware "plastic housing" making a new injection molded plastic case for the Chumby is expensive, in the range of $20,000 or more.

Two solutions were proposed, first 3D printing on Z Corp printers. This can be done for about $300-400 per part. It requires 3D CAD drawings. For $300 you only get one part, but the part will be accurate to the drawings. This is a good way to check parts before sending them somewhere like www.protomold.com. Protomold is a $20K solution but you can get a 1000 parts if you need them.

The second proposal was to use a thermal plastic like Polymorph, Friendly Plastic or Shapelock (all the same thing, $30).  But to make an accurate case with Polymorph you need a mold.

Example of free form part making with Shapelock:
http://www.micsaund.com/2006/03/13/plas … -projects/

Comments indicate that "RTV Silicone putty for mold making" would be a good choice for a mold.

While Googling around for Silicone putty I found this guy who is really into mold making and who happens to be in San Diego.
http://www.jgreer.com/, John Greer, 4401 Twain Ave. #26, San Diego, CA 92120,  (877)342-8860

Maybe a local Chumbian can give him a visit and get recommendations on good ways to do case mods. For example it would be very helpful to buy a prebuilt mold that had the inside half of the mold already configured to hold the Chumby hardware and the outside half was customizable.