You're probably looking at a run of less than 1,000 machines, so pricing has to reflect that. There's a lot of mechs on older games, many of which are not reproduced, plus you need to redo the wiring, etc. - there's going to be an engineering expense involved, not just assembly. Unless they're just going to use existing boards I suspect there would be some re-engineering there as well.
I think Stern could totally do it in the $4,500 range but why bother when they make more on the stripped down Pros.