Now take the money your saving and buy a good thermostat. You will have time to shop around for a pvc cage.
SOLID advice right here. I bought a cheap thermostat, and it did the job... but a month or so later, I broke down and bought a good one (Herpstat 2). Much nicer, and if I wold have went with a good one in the first place, i would have saved myself $50+.