One of the things about buying guns to hold their value or even to make some on is you need to buy quality. I doubt anybody is going to be getting in a bidding war over a Savage Axis or Taurus Judge.
Doesn’t hurt if you can pick up some quirky oddballs that end up not selling well. A buddy bought two S&W 296 hammerless 5 shot Lframe 44 specials years ago because J&G sales was blowing them out for $249. They’re worth about 8X what he gave for them. Same for the 32 mags that were not very popular. All the short runs S&W did for distributors back in the 80’s and 90’s command a premium with collectors, I wouldn’t be surprised if today’s special runs follow that trend.
But yes I agree, your run of the mill M15s and M19s and the like are probably actually cheaper today than when new as far as buying power goes. To make a comparison to the OP’s revolver selling for $250 in the 70’s, my dad bought a new 1979 F150 for $5450 pretty well optioned. $250 bought a lot more then.
Your buddy is smart, and doing what I've thought about but haven't.
Shopping the blowout sites for discontinued, discounted, retards.
When Ruger made the Super Redhawk in 10mm, my first thought were
"Who wants an artillery piece shooting a mid level round."
The next was, "Not many folks, until 10 years from now. Then they will bring
ungodly money from the collectors saying "They only made xxx of them."
Of course it slipped my mind, a more diligent fellow would be watching J&G and
CDNN for such opportunities.