For my OA Mk 1 it was $17k in 2012.
Pete suggested not replacing core. Well, it depends. If the core is balsa you have no choice as it will stay wet, rot and turn to mush to the point you would feel unsafe walking on the deck! If its ply or wooden blocks in the core it will not be as big a disaster.
But I for one take the view that if you are going to do a repair, then do it properly! It will pay off when it comes time to sell, if not in price then is terms of ease of sale.
I hear what you're saying Brian, but as the above posts, and your own, confirm, doing it properly is damned expensive. The solution I suggested is very effective, because the layer of marine ply laid down over the top fibreglass layer, after the teak is removed, then that sealed with a layer of glass, such as FF describes, does give a strong firm deck, and the only downside is the dampness is trapped between the glass layers, but in there it's not going anywhere, as long as further water ingress is prevented by a good glass and non-slip layer. You could then think of it as more insulation from heat and sound. In my boat that being done to the main deck was totally effective.
Unfortunately, the top flybridge deck where the PO didn't bother doing that, remained a bit spongey, but no-one ever went through it. I guess it's really a matter of how much money one is prepared to spend on a cheap boat - or walk away and spend a lot more on one without those issues -
or at least appears to not have those issues. Sometimes the devil you know - and deal with - might be a safer course..?
PS. They seldom used balsa for these cores, so the timber used is not generally completely mush. However, real tragedy, if you could call it that, is that a bit more money was not spent on these decks earlier, by using a synthetic core, and not screwing the teak down, but gluing it, as in later models. Think what problems that small extra step and cost could have saved down the track.