cost to own an inground pool

I had a friend ask me what it cost monthly to have a swimming pool in my yard, I said really not much I just do not know - my pool is about 20,000 gallons and requires some water each month which we get 10000 gallons each month included on our water bill for 45.00. The chemicals are probly about 18.00 month and I have no idea what the elect cost to run the pump 8 hrs a day. So my question is what does it cost to run a horse and a half pool pump 8 hrs a day. And yes I know rates vary but some of you engineers will have an average for this question.