Check out my new DIY vacuum forming website, www.vacuumformerplans.com

It's got links in the side bar to articles & threads on making good cheap vacuum formers, moldmaking, avoiding webbing (wrinkles) in vacuum-formed parts, etc.

Here's a movie of a simple vacuum former in operation:

Vacuum Forming with your Kitchen Oven and Vacuum Cleaner (2 min 56 sec)

It's cheap and easy to make, and works very well.