I had to replace the masthead sheaves on my old Catalina 27. They had been "sticky" for a while and, one day, the mainsail just wouldn't come down. So, I had to ascend the mast on the jib halyard to see what the problem was. There was a fair amount of swell, that day, so I wasn't able to get a clear look, but I was able pull down on the main and get it to come down.
To replace them, we decided to drop the mast ourselves. This went OK-ish. No one died and we didn't break anything. But, both sheaves were pretty badly corroded - enough that I am really lucky that I was able to ascend the mast without incident. Made me skittish about ascending masts, in general, though.
I don't recall why, but for some reason I needed to access the masthead again. Seems like I realized that I had done something wrong and needed to correct it. I don't remember. But, I didn't want to drop the mast again - it was enough of a hassle. The boatyard had a great solution, though. We just pulled the boat into the haulout slip, then came out on an articulating boom and brought it right up to the mast. The operator went up with me (probably for insurance), but I did the work. I think it costed me something like $150 - money well spent.
For a few reasons, boatyards are becoming increasingly expensive. But, $3000 USD is steep - you are right about that. But, if that involves a rigger restepping and tuning the mast, then that's probably about right. An additional $2000-$5000 to replace the sheaves is crazy town.
I would push back about the DIY issue. It isn't uncommon for boatyards to restrict what you can and can't do - like painting and sanding - often due to environmental issues. And, they often restrict who you can bring in to work on your boat. I think this has to do with insurance and limiting competition.
But, for that kind of work, it makes no sense. If the mast is down, you should be able to work on your own mast.
I would frame the questions like this:
"If I were in your boatyard, on the hard, would I be allowed to replace my own lower sheaves or, say, a cleat on the mast? What about a piece of deck hardware?" (This establishes if there is a policy that prevents owners from doing any hardware replacement on boatyard property.)
"If we removed the mast and I took it home, and came back with another mast, would you install that mast?" (This establishes that they remove and install masts as a standalone service.)
If they will remove and install masts as a standalone service, and they do not have a blanket policy against DIY hardware replacement on their property, then this makes no sense. You are simply paying them for that service and doing something which is otherwise allowed.
Of course, $3000 just for that service isn't nothing.
