Back in the golden age of gunmaking, when most of the work was done by hand, a rebarrel cost 3 guineas on a 100 guinea gun, or roughly 3 per cent. Fast forward to today, the age of CNC and certified steel etc, and the ratio jumps to 30 per cent. Something does not compute.

For 30 plus thousand pounds you can find a superb example of a Stefano Zanotti improved Holland type SXS. Improved in the sense of stronger lock up and rebounding locks. With superior finish and engraving to boot. See here an example with pinless locks. I shudder to think how much an English firm would add on for pinless locks!

https://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=513701

As for charging what the market will bear, that is a questionable practice. It leaves room for serious competitors, (those that can provide the same quality product at a lower price) to undercut you. And when that happens those that paid what the market could bear feel defrauded.