I suspect that the cost of heating a tank during the winter is somewhat overestimated. If you think about it, for any tank that is in part of the living area of a house, heating the tank also heats the room. It's a small amount of energy input, and a small amount of heating, but it should offset some of the heating requirements for the house. Basically, it's not just heating the tank.
That said, I'm using air powered filters wherever possible and shared lighting for some tanks (a 4" shop light goes a long way for a bunch of small tanks.) All told, 76W are running continuously for filtration and circulation, 150W are running 12 hours a day for lighting (some LED, the rest fluorescent,) and a 100W heater runs perhaps 2 hours a day in one tank. 159 effective watts being consumed at any time, 3.8kWh daily, or about $0.40 per day. $12 per month, give or take. I haven't noticed any major difference in my electric bill since I caught the shrimp bug in spite of adding 7 tanks. Again though, I intentionally am using the lowest cost/power options I can find and leaving the tanks unheated.