Temperature control for insulated area?

So I'm putting my house up for sale and have to move my frogs outdoors. I'm going to build an insulated area in the garage and add a heater to keep them warm (I'm in SoCal, so it never goes below maybe fifty even in the worst of winter), but I need something for temperature control. Does anyone know of something decent that isn't $400? This is just going to be for a few months at most, so I don't really want to spend that kind of money on something I won't use once this is done.