I did the paint job myself on my 400F tank after pricing good-condition used tanks, and calling around for estimates on a professional job. I spent about $250 on a HVLP spray gun and paint supplies (already had a compressor). I think it turned out really nice, but it took a lot of work! 90% of that work is in the prep. If you don't have a good surface to start with, it will never look good.
Here's a picture. This tank was stripped chemically and mechanically, smoothed and dents filled with body filler, two coats of primer, four coats of color, and three coats of clear.