I've seen them go as low as $400. (EDIT: quick ebay search: http://www.ebay.ca/itm/NJS-KEIRIN-Br...-/130759009720, I guess $300). But the whole njs thing is overinflated anyways, so it could easily be worth much more on ebay.

I've heard (dont quote this) that frames made by njs certified builders, not intended for the japanese circuit, don't get the njs stamp. So new frames shipped outside japan wouldnt be stamped.