A picture is worth what someone will pay for it. As Craft points out, the link shows the the dealer got £175 for his print but that doesn't mean that you can get the same for a similar one. The dealer might have bought a bundle of a dozen prints for, say, £50 and then put all twelve onto his website, with that one being the only one to sell. So although it cost him £50 to obtain the print, it was originally only 'valued' at roughly £4 (being one twelfth of £50).
I've seen similar prints, offered at country auctions, where the auctioneer hasn't even been able to get a £1 bid for the picture. Victorian prints form a very specialised market, with only a few people interested in buying them at present. I'd be surprised if you could get much more than a tenner for the picture.
Chris