If you look in my sig all but the 65 & the 72 are in one room. The biggest electric draw is the heaters, having all the tanks in one small insulated room contains heat, the cory tanks don't even need heaters, as the room temp is around 75F. I cut a heat register into the main trunk, the room is heated by my gas forced air furnace in the winter.
Next biggest draw was all the power filters & small air pumps. I recently converted to a central air system with one large pump that provides air for all the tanks. This pump pulls 60 watts, and I'm bleeding off around 1/2 to 1/3 of the air. This eliminates nearly 20 power filters, along with 8 smaller air pumps, and several powerheads.
I have no live plants, much of the light is provided by a window, and flouro lights that light 2 or 3 tanks per unit.
My electric increase with all these tanks was getting towards $80 monthly, since I switched filtration I'm down towards $50 per month. I'm looking into a small gas space heater, this will heat the whole room, which will save a lot during the summer months. A few smaller freshwater tanks can't cost more than a couple dollars monthly to run, lights for plants will increase this a bit.