Oh I dunno, what did they cost back in '73 - maybe that plus a 50% markup. Seriously though, why bother making all this retro/nostalgia crap, just concentrate on making decent, current motorbikes that people want, that would be my take on it.
Takes easy money off rich people. As a business plan it’s genius. By the numbers Ducati sell they are doing ok in selling the bikes people want, I would say.