My Dad recently built an amazing green house, and was able to get the glass and shelves at a Habitat for Humanity thrift store! He had to buy the lumber, but the glass and shelving cost him less than $40. I thought I'd pass this along, since I didn't know that Habitat for Humanity had a thrift store. I'm headed there tomorrow to see if I can find some shelving. Dad and I live in different states, but I checked the web, and they have stores in other states too. He said he was also able to pick up an attic fan there for moving the air, but got the heater, which aren't installed yet, at another store.
Here are some photos of what he built. I'm so jealous!