In ground, above ground, how many gallons is the pool? In Arizona most everyone and most every pool installer recommends 24/7 on in ground pools; it won't hurt anything as the motors are continuous duty motor. I don't know what it cost to operate a pool pump, I've never broke it down, but with AC, its minimal I'm sure because the electric bill at my house in Scottsdale with a pool pump, and 3 13 seer air conditioning units in a 6200 sq foot house with 4 kids was $329 last month and thats with hair dryers, coffee pots, washer, dryer, lots of interior lights, pool lighting, landscape lighting, etc.
Another thing it depends on what size pump you have, the smaller the pump, the larger the pool the more its going to need to run. Believe it or not a pool not circulated can get real stagnant and start to smell within hours and it can wreck havoc on the chlorine and PH levels, so keep an eye on it.