You posted: “I think it's a good boat if there are no major structural issues (with mast or hull) that I didn't see. Wonder how to "buy" this boat, take it to a surveyor, and then negotiate from there. I know that is not standard procedure though. Has anyone done something unusual like this in the past? How did you work it out with a private seller?”
I‘m not going to tell you what to do in your situation; it’s your money at risk. Here’s my experience:
When I bought my 34 footer, I first visited the boat (in the water) and spent the day looking hard at all the different systems and checking out the mechanicals. After liking what I saw, I went home and submitted an offer utilizing a standardized form, but made the offer “contingent upon a thorough marine survey”. By doing it that way it left the door open to additional negotiation, dependent on what the surveyor might find. I found a surveyor that was local to the boat and willing to do the wet and dry surveys. Unfortunately, the boat was 400 miles from me so I wasn’t able to be present that day, so I relied heavily on his experience and knowledge. He performed both surveys (on different days), with the seller agreeing to operate the boat and arrange for hauling (I paid the marina for the haulout, blocking and re-launch).
The survey was 22 pages and included many pictures, including those he considered items that were in ‘below average’ condition. It was VERY thorough, and I used the survey as leverage to negotiate the price to my satisfaction. Since the boat wasn’t local to me and I was going to run it the 400 miles to my homeport, the owner agreed to do some repairs to make it ready for water transit. It all worked out and the voyage home went well with no mechanical issues at all.
Although not pertinent to your situation, my offer also included the seller to provide a professional Captain to assist me in half the delivery voyage, which he agreed. It was a great trip and I learned a lot from him!