I'm currently using a homemade cooler incubator and although I'm only on day 12, things appear to be going well. All in all, I spent $10 to make this and that was for the light and the bulbs. Everything else was stuff I had laying around the house. It took all of 15 minutes to make.........I don't count the cost of the thermometers/hygrometers in the cost of building it because I can use them for lots of other things.
I got the styrofoam cooler from a doctors office I clean - they received medicine in them and I kept bringing them home much to my husband's chagrin - but I finally found a use for them! I'm actually going to go out and buy another light today so I can build a second one. Everything else I used is just stuff I had laying around the house.

I do have to keep a towel around the cooler because it is so cold in my office - but it's no big deal.
When I build the other one this afternoon, would you like me to take pictures of the process for you?