You could maybe list your measuring tools as "Post Apocalypse Gunsmithing Tools: No batteries required".
Old guys like us need the big digital displays to see the numbers. The people who like these 40 year old manual tools probably already have them, but they are good name brands.
Maybe have a look on ebay to see what they're listed at (or actually selling for, some have been re-listed for 40 years) and put together a list of trade items. You might find a survivalist wanna be gunsmith who will buy precision measuring tools that don't need batteries. That would be their best selling point, other than the quality, of course.
Before you list them for sale, take some baby oil / mineral oil and a soft cloth and actually clean the calipers. If they look clean, they will sell a bit faster. Sadly, I have no idea what they're worth but I think guntech is right again. You will probably struggle at $250 cash, but you might get that "value" in trade, if you're willing to take a used Norinco or something.