Well. I don't have a heater, yet. The cheapest we found that fit my tank was $97.
My house gets cold, but not my room (where the tank is). My room is usually very warm because my computer gives off alot of heat, not to mention I usually have my window and door closed all the time.
That temp is probably alright, however make sure it doesn't get too much colder. A heater is also nice for when you have sick fish and need to adjust the temperature to fight the disease better. For example, at your temp, it would take about a month to get rid of ich, at 30, a week.
Walmart has heaters cheap (the same one that Petco carries for $24.99). I just got one for my 10 gallon tank for $14.99. I don't know if they are up there (as in Canada) but you might try shopping online.