The temperature you germinate at can be important. Several people in this forum report success with temperature fluctuation in the 70F to 90F range. Search this forum on "temperature" to read the posts. There presently is no page in the wiki devoted to seed germination.
The cheapest heat mat you can buy is at the drug store -- for aches and pains. These typically have 3 settings. The lowest setting is usually delivers 85F. I use it for rising bread in the winter when the room temperature is too cool.
The heaters at the pet stores are often categorized by specific animals, because they have certain needs. All of them I have examined are regulated at 75F or higher.
The hydrofarm heat mats (
http://www.hydrofarm.com ) are advertised to keep the temperature 10 to 20F above ambient temperature. The ones I've tested maintain low 70's F in the garage where the temperature is 50F, and shut off at 80F when the room temperature rises. Hydrofarm also sells a temperature regulator for its heat mat which will keep the temperature from rising above a specified value. For many fruits and vegetables, the optimum seed germination temperature and scion rooting temperature is 65F (but apparently not for bananas).
Burpee Co. (
http://www.burpee.com/ ) and others also sell heat mats. Those I've tested are unregulated, performing similar (sometimes identical product) to the hydrofarm.