If I'm reading your question correctly, you need to heat the enclosure due to a defective under the tank heater? If that's the case, then as said earlier, you can use a heating pad. If you have a few bucks to spend, then go out and buy a few 70 hour heat packs.

One other bit of advise I'd like to offer. If you're on a tight budget while owning a reptile, try to put a few dollars away when you have it and use ONLY in the event of an emergency FOR THE REPTILE.

If you have a good relationship with a pet store (local mom and pop store not petsmart type store), maybe you could ask them to sell you a UTH on credit. Telling them you will give them the price of the UTH and an extra $5 next week.

You need to be able to take care of your reptiles. Having an emergency fund is required.

Good Luck!
Jim Smith