If I'm not mistaken, one of the hot rog mags did a car with a roller a few years ago - and it did look half way decent --- from 25 feet and at 50mph.
What I'm saying, you get back what you put into a paint job. What you possibly haven't considered is the cost of doing a car paint job using decent middle of the road materials. Automotive paint, a national brand in anything but black or white plus the primers, fillers, thinners, tape, sandpaper is in the high hundreds of dollars and then some with pearls and metallics doubling that number. Then there are the labor hours to prep the body which can be minimal to hundreds. So with that said, a day of work plus $50-$100 of materials to build a booth - dam' cheap