I finally have a thermal vacuum chmaber (TVC) design I like. It's called Near Space in a Can and it will sell for $250 as a kit plus shipping (minus the vacuum pump since it's cheaper to pick that up at the store than sell it).
The TVC has a diameter and depth of nine inches. It's exterior is packed with dry ice and it's then pumped down. Inside the environment approaches near space conditions. I'll add radioactive materials and evnetually UV sources to more faithfully replicate near space.
As long as you're willing to pay postage, I will expose experiments (not living objects, please) to the chamber at no other cost. Eventually I'd like to have several of these available for amateur testing.