Obviously the higher you set the thermostat, the lower your electricity usage/bill will be. I think what you are interested in is how much it cost you typically to set it at say... 75 versus 79. I don't know the answer but think I have seen charts like that for various sized homes in my area. Seems like the local power companies put those out? Might find something on their website.
found this...
http://www.achrnews.com/articles/94014-set-up-a-few-degrees-for-significant-savings
Go to any Web site for energy savings information and the most popular advice is to lower your thermostat in the winter and raise it in the summer. One of the reasons this is such a common tip is because it is easy for a homeowner to do, it requires no initial investment, and the savings can be significant.How significant? Many sources quote one percent to three percent for each degree you adjust the thermostat. But these estimates apply more to winter savings than summer savings. Air conditioning savings can be much greater than this.
[h=2]Reducing The Temperature Difference[/h]Of course, the thermostat setting is just one of many variables that determine how much it will cost to air condition a home. Total air conditioning costs accrue from conductive heat gains, infiltration, radiant gains, internal gains, and latent load. When we discuss thermostat settings, what we are really focusing on is the temperature difference between the outside and inside that is driving the conductive heat gains. Solar gain and the latent load are not as sensitive to the temperature difference and may not be affected by a small thermostat adjustment.For this discussion I will assume solar gains have been minimized with window coverings and the latent load is not unusually high.
When you air condition your home to 75 degrees, and if it is 90 degrees outside, this is only a 15 degrees temperature difference. Each degree of this temperature difference represents a percentage of the total cooling load. Raising the thermostat 2 degrees lowers the temperature difference between the outside and inside by 2 degrees.
Since there are only 15 degrees total, a 2 degrees change represents a large percent of the total load. And, most hours of the day are not 90 degrees!
For all the summer hours where the temperature difference is only 10 degrees or even 5 degrees, 2 degrees represents a very large percentage.
In the Midwest area you could save about 10 percent to 15 percent per degree, for the first few degrees you set up from 75 degrees. One way to visualize this is to look at a chart of the average cooling load for each summer day. Cooling degree day data charted for Indianapolis will show us a pyramid of increasing daily cooling loads, starting in April, rising to a peak in July and decreasing back to zero in October. If a thermostat is set low enough, a home might air condition from April to October, or theoretically on all the days that have one or more cooling-degree day.
If the thermostat is set higher, a home may only cool from June to mid-September. A very conservative family, one that "...turns on the A/C only when road tar is bubblin' and the fish are swimming upstream through the front door," may only cool for a few weeks each summer.