Would would be market value assuming excellent condition and upgraded wood?

They depend alot on opetions, like wood grade, casehardened components, quarter rib, etc. Somewhere between $4,500 and $6,500 for most builds.

Yep. I agree with Biebs' range.
A bit under 2/3 of replacement cost seems to be the maximum number for one in as new or 99% plus condition these days. It's mostly about the wood, second in line is caliber popularity. Ones with boring wood seem to struggle to bring more than half of replacement cost.
Got a picture of the wood bluefish?
Great caliber.

PM sent to bluefish.

Would need the gun in hand or a detailed description, but Id bet the above quotes are mighty close..