We had a deck guy over to have a look at our situation and he agreed with the last guy that it was a 10 or 20 grand job.

I asked him if he'd let me know if he's going to do something similar on another boat to give me a ring and let me come be his assistant and he said he would.

He did give me some reason for optimism though in that I'd been really puzzling over how to deal with having the surrounding core open to the elements once I'd cut open the rotten part. He said that wouldn't be an issue if I used his approach since he'd immediately build a watertight barrier against that perimeter as soon as he had it opened up.  

This is sure going to be a learning experience.