Look at http://www.ponoko.com/.
They laser cut a variety of materials. Wood, metals, leather, and acrylics. People have made cases out of the acrylic which will probably cost you $30-50. Depends on the size of the source material and the amount of time it will take the laser to cut.
The trick is that you are cutting flat material. You will need some skill at drawing vector graphics. There are plenty of examples you can follow. And InkScape is available for free.
Sparkfun Lamp (probably not the kind of case you are thinking):
http://www.ponoko.com/design-your-own/products/sparkfun-mini-lamp--4742
Makerbot design (shows how to take the "flat" pieces and turn them into a box.):