An acquaintance has a pair of James Purdey & Son marked 12 gauge snap caps acquired in the 1970s. He believes that he paid 50 pounds for them then. They have never been used. Could they have cost that much then, and what would a set cost today?

Might be worth seeing what Purdey's currently charge although even there I think it would not be that much even now. Purdey's know how to charge even thogh they would have been mass produced and made with any number of Gunmaker's names on. £50 in the 70's, allowing for inflation, would be close on £300 to £400 in today's terms. Lagopus.....

This is the link to their site but the snap caps listed don't show a price. Lagopus.....

Google "Purdey snap caps" and you should get some websites that list the price for a pair of Purdey snap caps

Vintage purdey caps come up for auction today for 50-70 GBPs. Sometimes 150 GBPs will get you 4-5 sets of known tier 1 and tier 2 maker's caps.