I suggest a Zoo-Med UTH. I got mine for $21 (10-20 gallon UTH) at Petsmart, but I bet they have it cheaper at other stores near you.
For a thermostat, I would suggest a herpstat. If you cannot afford a thermostat, the best to get would be a rheostat/dimmer until you can afford a thermostat. I did a test on a 10-20 gallon UTH to see how hot it gets so I took the snake out of the enclosure and turned on the UTH and it got as hot as 113F in a little amount of time and it was still rising so I really suggest a thermostat or at least a rheostat to control the temps.
I think getting a thermometer would be best. Get a digital thermometer, too. Digital thermometers are more accurate at telling the temps. I bought mine for $8 at Petsmart, not too bad of a price. You can try to purchase an AccuRite (not sure where to get) which tells temps and humidity which is very helpful (also digital). I'm sure someone on here could tell you where to get AccuRite, it only costs like $15, too.