it's not a racing kart, and not yet as collectible as the original Rupp would be,
but it's the closest rupp replica there is, and being a D301 not the most common either
(A-Bones are far more popular)
while 500 seems a bit high I think if it comes with the original turbines it's a steal!
if it comes with vintage kart wheels (original nylites, hands, go power or such) that'd be a fair price.
if it comes wth mancos I'd try to talk him down to 400-450
if it comes with azusa tri stars or other still available wheels another fifty less IMHO.
(can't tell by the ics you posted)
PS most shockingly.. that Ryan on that tiny image looks oddly like "our" Ryan did
that had me stunned a second