Dimmers work great as long as you have constant room temps no fluctuations typically 80º is what most use. Although depending on your house and location that can be very costly as well. Home thermostats can be made to work but by the time you have added the parts needed hard wired it to the main power and 100 other things you might as well buy a herpstat as it will cost less. On off style ones work best with a large thermal mass or a no direct heat as you are speaking about a rack (non direct heat source) they typically work resonably well. The Johnson a-419 you might be able to get off the shelf from a HVAC dealer.Same for the ranco ect-111000. A hydrofarm you may be able to find at a greenhouse supply or at a hydroponics store. I agree that you need a week to work the bugs out before adding animals to a new rack things can be quite squirrelly at first. Racks really like stable room temps so an oil heater usually solves most rack issues but cranks up power costs, racks are pro tools and generally need pro solutions.