I put a fan on my roof and it really doesn't do much for the electric bill. Maybe 50 cents a month at worst. But it makes a huge difference in the house temperature. I went from running the a/c a few hours a day to only running it when it gets really hot a couple of times a month. It doesn't get as hot here (WV) as you get though but I am sure it will help reduce your a/c load way more than the small amount of electric it uses.
I would also paint my roof white or chrome plate it if I lived in AZ
