For my 16,000 gallon pool, it's around $15 per month with chlorine and a small amount of acid. However, I have a mostly opaque electric safety cover so even though the pool is used daily, the chlorine demand is around 1 ppm FC per day or less. If I had no cover or a clear bubble-type cover and more sunlight exposure, I'd probably have 1.5 to 2 ppm FC per day so costs would be up to $30 per month.
I use winter rain overflow to dilute the water each year (keeps the salt level down as well as built-up organics) so need to increase CH, CYA and borates so that's around $60 or so. Our swim season is around 7 months and chlorine usage is minimal during the off-season (around 1 ppm FC every 2 weeks) so total annual cost is around $165 in chemicals. The real operating cost for the pool is the pump electricity cost when using solar as annual cost is around $700, but our electric rates are high at 40 cents per kilowatt-hour marginal rate.