WOW!!!!
I thought ours was high. We are low income and sometimes we just can't afford to pay our natural gas bill and let it get turned off so we can use the money for other bills. In the Summer we don't use much but if we average it out the bill is still close to $100 a month. We have elec. water heater and dryer. The stove and other stuff that is gas is hardly ever on during Summer either.
It we get a cold spell we plug in the electric heaters, one is a fan blowing over hot coils and the other is a radiant heater that looks like a small radiator. I like the radiant heater for smaller rooms better. They are great for super warming the bathroom or a bedroom. They stay in the medium range and I check the wall around the outlet often to see if the outlet or wall is getting warm, signs that the unit is using too much power from that socket. If it is set on medium heat it should cycle off and on like a central unit would. I find that it keeps the rooms warm and comfy.
In you situation I would think keeping the house cooler during the day and a bit warner at night would be ideal. You can put on some extra clothes for daytime and then be comfortable at night. I just hate getting up and sitting on a cold toilet seat.
The electric heaters would, of course, move some cost in to the electric bill but electricity may be much cheaper per unit.