GW, my value method gives the following result. The H&H name has Brand Value level one (top level of value added for brand), BV1. The Original Quality grade for Royal guns is one, OQ1, the best except for extra embelishment (extra finish). The Current Condition level seems to fit reasonably well within the follow ing descriptions: "Limited use - slight finish wear, little shooting" = CC2, "Significent use" = CC3, "Heavy use, but no abuse" = CC4. BV1-OQ1-CC3 = $20,915 for a 12 bore shotgun. Double rifles seem to have a premium value of 2X to 3X for dangerous game/truly big bore guns. So, we could take a guess at $42,000; little more if CC is better, little less if the rebore/rechamber is questionable (I doubt there will be much question on H&W work, though).
Most of the big auction sites have a web archive of recent (past few years) activity. I'd suggest a bit of research for comparables on Holt's, Bonham's, Gardner's, and Julia's sites.
Beautiful gun!!!
DDA
