The value of money halves about every 20 years. So a gun that cost £150 20 years ago would be £300 in today's money - without considering the points already made above, e.g. potentially higher manufacturing quality, and rarity, than can further increase the costs. Vintage guns are obviously a good example of all of these effects.
The cost of something 20 years ago has little to do with the market price today - I'm pretty sure you wouldn't let me buy your house off you for anything like what it cost 20 years ago
Always looking for any cheap, interesting, knackered "project" guns. Thanks, JB.