As usual, Rocketman's calculations are really, really good considering he is pricing the gun from a formula, sight unseen.

I'd say a fine lang (best) sidelock ejector with original barrels is an $8000-$15,000 gun. I'd say the gun you describe with replacement barrels is in that $3800-$5800 price band because of the work described.

Excellent guns made by an excellent maker (and Grandson of Purdey) for a very reasonable sum of money. I'd go for it and shoot it regularly!