I would be happy to refer you to a great agent in Elk Grove .
Keller Williams Realty
You might call the utilities for the average cost for a specific home, as Erin has suggested. The other idea is to address the specific problem of your friends and have them call for a free energy audit. It may not be so much that it's a two story as some of the other factors mentioned. It's also a good way to work towards making their home 'greener' through some little steps.
There are a few variables to this question. Do you have new dual or triple pane windows in the house. How old is the hvac unit. Has new insulation been installed What type of roof material. These are just a few items that could change the energy cost of a home. I think in general that most 2 story homes are less efficient but there does not have to be a big difference between the 2 floors if the home is maintained properly.
was only one air conditioning unit, or multi-unit. If only one unit, and the house is not insulated extremely well, that utility rates would be higher in a 2 story. If you have a separate unit running just upstairs, then
maybe not as much of a difference as you could set them independently.