I don't know the exact cost because it was a gift, but I think it was in the $50 range. Its a 2,000 watt heater, my fish room is about 120 sq. ft., so not a large space. I've had as many tanks as 35 tanks in there, but I don't think the number of tanks really factors into the equation, the water adjusts to the ambient temperature independently I believe. I set the heater at 74, it kicks on when the temp hits 72. I'd say the tanks always stay at 70 or above, but I don't really monitor them anymore. I don't know how often the heater runs since its set on a thermostat, and I couldn't say how much the electricity costs to run it, but I'm sure its much cheaper than having a bunch of heaters in the tanks.