Tim, no offense, but I think one of the stupidest ways you can try to save money is by buying a used heater. The heater is the only piece of equipment on most fish tanks that can fail and kill the fish, and its the only piece of equipment that is guaranteed to eventually fail. Heaters are ticking time bombs, and when you buy a used one, you're buying one that is god-knows how much closer to its expiration date, and you don't know how it was used, handled, etc. before.
Heaters should always be bought new, and only reliable brands -- no off-brand heaters, please. On higher end tanks, they should absolutely be plugged into a reliably controller. And, they should be replaced at least every 2-3 years.