From what I've gathered, I believe ARC makes (or made, dont know if theyre still making them) very high quality ribs in the Massachusetts area. Military contract, really heavy duty. I've only seen one for sale. It was in the New England area this past summer. 18 ft in great condition with a newer 90 hp, trailer, etc. Don't know the year, but looked to be in very good condition. He was asking 9000, went down to 7900 and then disappeared, I assume it was sold. In the US, it's really hard to determine a good price because ribs in general are so rare.
also:
http://rib.net/forum/showthread.php?t=12378