I paid around 100 for utilities in a place that was smaller, 565 sq. ft. last year, but I didn't have central air, just a wall unit AC so that will cut down on cuts dramatically.
You might be able to look up how much the current tenants are paying right now, I know for my utilities website I can check past bills to see how much power they used. It also depends on what you have and your habits, if you keep the AC set at 65 degrees 24/7 then expect to pay more, but if you're smart and conserve you can cut down on costs a lot. Don't leave tv's, computers, etc. running all the time, take shorter showers to cut down on water usage, etc.
What else do you need to know?