That's one good thing about a QUALITY firearm. If you buy one, and keep it stored properly, chances are very good that it will increase in value over the years.
Way back in 1977, I bought a nickel Colt Python with a 4" bbl. Cost me $350.00 + tax. If I still had that same gun today, NIB, I could easily get close to, or approaching $2K......give or take.
But, it's all about buying a good brand. Many will debate which is a good brand. It might be easier to list the not so good brands.
Taurus will not appreciate. Ruger is kind of a crap-shoot, but historically will not appreciate. Rossi is junk and not really worth what they get when purchased new.
I could go on, but just pay attention to the lessor known brands. Stay away from them.