If the boat is in the same condition as the photos, and the sails are in good shape, standing and running rigging are not original, have it surveyed. If it comes back with flying colors then it is worth what you think it is and offer him that much.
If it where me, and the all of the above was good;
I would set up a meeting with the owner and surprise him with an offer of 15K in cash to close immediately.
Three $5000 wraps of hundred impress a lot of people unless they work in banks or casinos.