"so my guess is that they will continue to charge ridiculous prices as long as people will pay them. I can see a couple thousand, maybe 3 thousand for a really nice shotgun, but more than that is just sillyness."
Did you come here to get an answer to a question? I don't think so because your mind is made up on the subject and you're not listening to the answers.
"which tolerances in a shotgun are critical to make it more accurate, durable etc?"
Durable? Talking about SxS and O/U shotguns, it's the hinge area that weakens, stretches, and fails. (That's if the trigger doesn't break first or some other part like breaking firing pins one after the other.) Better designs cost money. Better steel costs money. And better steel requires better tools to work it.
Going back about 5 years before WWII, my father bought an Essex SxS 16 ga made by Crescent for a big hardware store in St. Louis. By the time he left for the Pacific, the hinge was loose (shot loose, off the face, by whatever name) and the gun was junked by his brother. It worked fine for 5 years of upland/mountain hunting in the Blue Ridge, but when it started falling apart it couldn't be fixed at a reasonable price.
In the early '60s I got a brand new Fox Model B 12 ga. SxS. It was just plain clunky and heavy and unweildy and it kicked, and the M/F chokes were more like F/EF and just shredded quail and rabbits. I was a disappointed 13-year-old. My uncle sold it to a guy at work and I learned another lesson. I should have bought a 20 ga. Model 12 like my father's.
You keep believing what you like, but you'd be wise to listen to the voices of experience.
Even my father, with his love of the Win Model 12, could appreciate a nice double when he was in his 80s. They feel and handle differently. He paid $2400 for this 28 ga. Guerini Woodlander 6 or 7 years ago. It's not even handmade, it's machine made.