It really really depends on the area of the country and the cost of living. For example, in minnesota we have no AC in our house but our heating bills are crazy in the winter, and in FL you have the opposite.
With the way gas prices are going, I don't think there is any way to predict what your bills might be 7 years from now. I think the best course of action would be to live frugally and save as much as you can now.
Suzan, mama to DS 9-18-07 and #2 EDD 3/4/10 GIRL!.