I leave a Fluker's min/max combo thermometer and humidity gauge in the cages to measure ambient temps, and use a temp gun to check the rest of the temps as needed. Thermostat handles the rest.

A short term, less pricey option than a thermostat is to pick up a rheostat or a dimmer switch. You'll have to manually adjust it (after a week of decreasing the temps for summer highs and then increasing them at night to keep things steady I was sick of it and just got a thermostat), but it'll do in a pinch. They range between $10 and $20.

We also carry simple analog thermostats that are only a few bucks more; again, an option for the meantime while you figure out exactly what you want, how you want it, etc, and are ready to invest in the good equipment.

-Jen