Doesn't seem that high considering they have been warning everyone of huge rate increases for over a year now. I have gas heat but have an electric window AC, my power bill for a month averaged $300 over the summer(which is about double what I paid previous summers). I am in a studio apartment too.

Also how old is the electric heater? ... They eat power worse than an AC unit does, especially if they are on the older side... Hopefully it isn't a wall unit, even brand new those things are terribly inefficient.