If you like soldering, look at the Jaycar kit KC-5225 or a kit from Oatley Electronics - K252 - DC MOTOR SPEED / HOT WIRE CONTROLLER KIT AUD18. I've succesfully used both of these.
There will be ready made kits that you will be able to buy, I'm sure.
This thread gives some information:
http://www.iceinspace.com.au/forum/s...ead.php?t=8514
Search "dew heater controller" for many more threads.