I think he was asking about a single color, not single stage.
One of the best custom shops in my area is also a paint supplier. They only use and sale Matrix. I'm an amateur but have shot just about all the brands and have been very pleased with this line. Since I am going all black I saved a little on the base coat as Matrix has a "stock" color that requires no special color mixing. As an example- the black b/c kit cost me $150 for 5 qts of RTS product. In comparison the quart of "Argent" for the grill cost me $85 for just the base. My point being that you can save hundreds of dollars by using a reputable product and researching within that line itself. Any work you can do on the car yourself saves a bunch. The one post listed $72 an hour for shop time. That adds up quickly, too quickly for me and that's why I do my own. My car isn't going to Barrett-Jackson. But it will be done right and no one will be able to say "Oh, look, you must have used the cheap stuff." :)
As an aside- Prep work is everything in the final outcome of a good paint job. To me the gun I use is next. On the advice of the paint shop owner I purchased an Iwata LPH400. A little more money upfront but using it eliminates the need to cut and buff the car. I use my old DeVilbiss Finish Line for primer and Iwata for base and clear. Since I will be doing more than one project it was well worth the cost.