There are TONS of homemade incubator threads in the DIY forum. The first incubator we made was from an RV fridge (small, held 8, 6qt tubs) with 11" x 3' strip of flexwatt, a wired computer fan, and a Herpstat T-stat. The next one we made (and are using now) is a Pepsi cooler.
Here are some pics. http://ball-pythons.net/forums/showt...-New-Incubator