As others have stated I wouldn't recommend a "cheap" thermostat either. It is one of the few things that can cause alot of problems rather quickly if something goes wrong. Especially if as RichsBallPythons stated it fails in the on position!
We just picked up the Herpstat 4 for our racks and highly recommend it. It's very user friendly and though it is alittle expensive up front the fact that it will control 3 racks and an incubator for us actually makes it less expensive than individual thermostats for each unit. GL