A dimmer is just a basic plug in lamp dimmer that you can get at Lowes or Home Depot for about $10-$15. They look something like this:
http://ball-pythons.net/forums/showt...t-Instructions
If you are looking for some inexpensive thermostats, you can check these out:
http://www.amazon.com/Hydrofarm-MTPR...1529683&sr=1-7
If you need to raise the ambient temps in your tank, you can try covering the two ends and back with foam board or cardboard to help insulate it. You can usually find foam board at Wal-Mart or Target in the school supplies section with the poster board. It will also help if you position the lamp about half way between the center and end of the top, and cover the exposed screen with aluminum foil.