Part of the problem is that you are looking at two different things that only have appearance in common. The British sidelocks you are looking at has four to six decades plus more use than the Spanish sidelock. Normal wear and tear will make the pool of desirable British candidates much smaller to buy from. Then you are looking a a much later Spanish made gun with little or no major long term use. Apples to oranges instead of comparable items. And it is the equivalent of a reproduction to a classic gun comparison.
It would be like trying to find a Parker 28 ga. and comparing an original Parker to the later Japanese made Parker 28's. Both the same, but vastly different. Find a high condition original Parker 28 and you expect to pay a a lot more for it than the later reproductions. Has to be the same with the British gun as well.
Dig is right if you are looking for the most gun for your buck think box lock ejector for the money you are talking about. They are still some great values in them for the money. Otherwise just buy your Spanish gun and enjoy. It comes cheaper for a reason and the resale value, which you are judging it by reflects the lower price. The Spanish gun will handle your shooting needs as described with a wider range of ammo.
I shoot these old doubles because I like a link to the past and the history they bring to mind. It if vastly more efficient to buy a camo auto, screw in a choke tube, load three and go bang, bang, bang. I rather spend a ridiculous amount of time thinking about which fixed choke two shot option to use for a shooting opportunity. Enjoy the ride and half the fun of buying a new gun is looking at all the different options out there. Who knows one of them might just talk to you. More than one gun I own was bought while I was looking for something else. Half the fun as I said.
