I have a very basic system on my beardie box that turns a muffin fan on when the enclosure temp hits 90, and turns off when it drops to 88. It would be a simple matter to turn a light bulb or CHE on or off instead of a fan.
I think the whole shebang including fan, thermometer w/probe, controller, etc. was under $50, and a good chunk of that was the fan & stuff you wouldn't need.
If you have trouble finding what you need, call them on the phone, and explain what you're trying to do. We were clueless, and they were very congenial and helpful setting us up with the components we needed.