I'm planning to use arduino to make a reef controller and it has the ability to do this. Arduino board ($30), Temp & Humidity sensor ($10). Add a couple relays, spend some time programming, and you would be set.
I haven't priced out relays completely yet, but I think what you (or I) would need is $6-8. Total price is probably between $50 and $100 by the time you factor in wires, housing, etc.
What else can one do with arduino? Control LEDs, monitor PH, temp, or anything else that has a sensor, ATO. My understanding is that the possibilities are limitless.
Just thought I'd throw another option out there.