It is my experience that in an average 2300 sq ft home your bill could range from a high of 270 and low of 90. Keeping your thermostat up near 80 in the months of July August September will help a lot. Being as efficient as possible will make a positive dent in your heating and cooling bill. Find a temperature you are comfortable with and don't continue to play with the thermostat.
Much will depend on usage, property size, etc.; consider contacting the local utility company and ask for an estimate; if referring to a particular property ask the current sellers, or any neighbor(s) with a similar property...
Wide open question based on the house size, style of living etc. The lower end in an occupied house would be in the $200 range up to $500 for a large 2 story home. I know people that get by on less and others that pay more but I suspect a lot of bills are between $200 and $350 for decent sized homes that are used.
The above is for the peak demand summer months, remember we don't have much heat demand so our season is flipped compared to many other areas.