I agree with most of what Starmom has said. I would like to add a couple of things though. If you have the tub in a room that maintains a constant temperature, you could get by with using a dimmer for the UTH at first. As long as you can maintain a stable external environment, the dimmer will keep the internal temps stable until you can save up to get a thermostat.

As far as where to get them, I know everyone in general will say to avoid Petco, but that's where I got mine. I would agree that MOST Petco and PetSmarts are crap, but there are some good ones out there. I would say to go look at their snakes and talk to the herp specialist (if they have one) at the store and get a feel for their knowledge. And ask questions, like when did they last feed, if they have fed. What are they feeding, f/t or live. The herp specialist at my local Petco is a member on this board and a friend of mine and I know that he does the best he can (within Petco's restrictions most of the time) for the animals while they are there....