Why not go with Flexwatt? I would wager that it's more inexpensive than even a cheap aquarium heater (not including t-stat, but you need that anyway.) Here are some pics of my incubator from this season that worked stellar. I had 2 feet of 12-inch flexwatt in the bottom. I then put some water-filled pop bottles for ballast, that hold the temp. of the FW and store heat and help evenly distribute it. Then the light-crate went over that and acted as a shelf for the tubs.