As a Florida transplant myself, with a 3 year old 2100 sq ft house, I'll give you the gist of what we've seen for the last 3 years. Our air conditioning is electric, our heat and hot water is gas, so which one is higher depends upon the time of year.
Summer:
Temp in the house around 78
electric bills can run around the 140s, highest ever 175.
Gas bill during these months around 20, as low as 15.
Winter: Temp in the house around 74 (It's not as bad, because the humidity is lower, so you won't feel as cold. Cold, but not AS cold.)
Gas bill hovers around 150, although one bad February, we hit 200. yikes!
Electric bill still hangs out around 50.
But, being from FL, I don't do cold very well.
We tend to budget for an average between the two of about $200 a month. We've just installed programmable thermostats, so hopefully this will help, too. If you need any other advice as a FL transplant, just pm me!