I'm guesstimating, but I would think that your bill without the ACs running would be around $70 to $80 a month.Probably less. Widow AC are extremely inefficient, and that's whats upping your bill. Take the tanks out of the equation, and I would think your monthly bill would be $45 to $50 a month. I'm guessing, but having paid bills for quite a few years, and living in apartments and houses with and without tanks, I think I'm pretty close to what it should cost you.so I live in a second floor apartment. It is about 815 square feet. I run the two ACs bc of the heat wave and the pets. The only other big appliances I have are the fridge, a dish washer (which doesn't get used often), and an oven. My bill this month was $145. This is the first full month I have lived here and had all my tanks running. The previous month was $40. All the tanks where moved in last month exept for the 90g. My buddy was doing work on the place and had his power equipment, but i don't know how much they ran the AC. When I moved in I thought I had the AC on for the last two weeks of June.