The summer months are cheap - we have an in-window AC unit but rarely (maybe twice a summer) have to use it. We regularly pay between $60 - $70/month between April and September. Once it gets cool enough to need the heat on at night is when the price really starts to get expensive: In the coldest months (December - February) we've paid up to $270/month to Northwestern Energy (gas and electric combined). The rest of time time it costs us about $170/month.
It varies on the size of the property, type of utilities, number of people and ability of the occupants to be energy efficient. The listing I have at 52 Arrowleaf Loop is very efficient with a woodstove to keep everything nice and toasty! If you have more specific questions please let me know.