gm32:
Welcome to TFP
Given a pool that is already in place, is structurally sound, and all equipment is in good working order, the largest cost components are energy-related (mainly the pump) and pool chemicals. What about heat? If the pool is heated with natural gas and you're like me and use it primarily to extend the swim season at both ends (spring & fall) then the heating cost over the course of a year is negligible.
As you read below, keep in mind that my pool is kept operational year-round even though we do not swim from Nov - late March.
Let's first focus on the pump. First thing I would do is read this article
http://www.troublefreepool.com/pool-school/pump_run_time and then begin experimenting with pump run times that work for your pool, noting that you may need to make slight seasonal adjustments. Most pool owners tend to run their pump longer than needed (myself included before I switched to BBB). My pump run-time cost for the period September 1, 2011 through August 31, 2012 was $265 which averages ~$22/mo @ an average electric rate of $0.10 per kWh. Note that it will be a bit higher during swim season and during periods of below freezing temperatures due to freeze guard protection. OTOH, during late fall and a good part of winter when temps are above freezing, I can go the better part of a week without running the pump at all.
Note that I have a single-speed pump which is an energy hog compared to a 2-speed or variable speed pump. When it comes time to replace it with a new one, I will only consider 2-speed and variable speed pumps which will lower my energy costs further, given relatively constant water turnover and electric rates.
Now the chems: My chemical cost using the BBB method for the period September 1, 2011 through August 31, 2012 was $436 which works out to an average of ~$36/mo. Likewise, the monthly cost will be higher during the peak of the swim season mainly due to higher chlorine usage (bather load, sunlight, & water temps). My chlorine usage dropped dramatically after Labor Day even though I continued swimming into early November.
So, in my case, I'm looking at an average monthly maintenance cost of $58/mo (energy & chems). Other than that, I have had to replace the in-line pool cleaner filter and the occasional hose or fitting for the Polaris. Nevertheless, I would recommend putting some money aside each month for those "Once in a Blue Moon" expenses such as replacing a pump, heater, surface refinishing (should get at least 15 years on this with good pool maintenance), etc.
For more details, you might want to check out my experience on pool maintenance costs under BBB vs my prior method which I have dubbed The Pool Store method:
http://www.troublefreepool.com/bbb-saved-me-over-1-400-in-the-first-full-year-t54033.html