I live in south Louisiana, I have a black car, and the only time I use the A/C is when I have passengers, which is rare. Definitely shop around, and unless you've got known issues with the car, I'd say it's cheaper to keep it.
That being said, I had a Nissan van that the A/C went out on at least 3 times, and the last time we got rid of it. Wasn't worth the hassle to keep repairing it. We replaced it with a Dodge minivan... that the tranny immediately went out on. So you know, 6 of one, 1/2 a dozen of the other.