There's a shop in Northern California that does a lot of work with FFR's. I've never used them, but here's their website:
http://www.streetrodpainter.com/
By the way, if 439 hours is correct for labor, then at $50, that would be $21,950 for labor, unless I'm missing something. Also, what's included in final assembly? Did this include any suspension and/or engine installation? In what area of the country are you located? That would make some difference.
At $15,000 ($12,000 for labor and $3,000 for paint and supplies), if the paint is nearly flawless and show quality, depending on location, and depending on how much body work was needed, and probably a few other caveats, then I don't think that $15,000 is totally outrageous.
Edit: Here in the SF Bay Area, I've heard and seen $15,000 (for paint only) quotes for mid-year Vettes.