You can check out http://www.henry.com
There are some good products out there and then there are some better ones. I am not a roofer, but I have done some roofing and have two more on the slate to do later on this year. For a flat roof, I would recommend an SBS modified premium grade membrane. This is not felt and it is waterproof as soon as it is installed. Then apply the cool roofing products that were invented specifically for Arizona. These do have to be resealed every few years, and I know several folks who have just done this. With this method you have a waterproof membrane with a waterproof sealer.
Another good product is the Lo-slope self adhering product that Henry sells. This is applied by spraying a primer through a pest sprayer and then applying the roofing product. It says to cut the product in 15 foot sections and by all means, do so. This stuff goes down fast. I did a roof a few months ago and I am very impressed with this new product.
$8000 for any roof that is not masonary is highway robbery!!!
If you do find the right roofer, he will probably be able to do a roof for about what it would cost you to buy the materials and do it yourself. There are some good roofers that don't have huge companies and big advertisements. Check the want ads and the penny saver and then ask the guy for references and call them. Good luck there:)
If your roof has felt or a damaged or improperly installed membrane, you will be chasing leaks forever.
Don't take much advice from folks at Home Depot. They talk big and can be very persuasive, but the ones that work in the roofing section are generally dumber than a bag of hammers. If they actually knew something about roofing, they would be roofers!!! I have been given bad advise on several occasions.