It looks like more of an auction piece because of the extensive engraving.
I could see that Paterson selling for $650-$850 or more depending on how many folks are bidding on it.
Remember that with live auctions there's a buyer's fee and a seller's fee that both the buyer and seller must pay that's a percentage of the final auction price. Neither reduces the gun's overall value, but the fees do reduce the amount that the owner receives and increase the amount that the buyer pays. The buyer's fee can effectively cause a person to bid lower.
It looks like a very beautiful and desirable piece. Thanks for sharing the photos with us