Good question, I'd like to see the answer from more knowledgeable firearms enthusiasts.
Likely because partly what is considered a "good" handgun advances with the state of the art, partly modern insurance and regulatory requirements drive up modern manufacturing costs, and partly because of market dynamics for the use cases a handgun is put to. If you were mass manufacturing a mid-19th century handgun, with no improvements in its tech or metallurgy, without having to pay for the operational insurance and regulatory overhead costs, and it was accepted by the firearms-purchasing public in the same per capita adoption rates as back when it was originally produced, I can easily see it being a lot less expensive. But the purchasing public seems to seek specific characteristics in modern firearms, these characteristics don't appear to align with "use old tech", and this tends to set a floor price from what I can tell as a casual user.
Interestingly, replica mid- to late-19th century handguns sell for around the $600+ USD mark in the US, for the enthusiast market. Well-cared for, lightly-used firearms are reasonably close to quality as new for most non-enthusiast level users, and even many enthusiast users. So if inexpensive is what you are looking for, a used firearm from a trusted user goes for roughly half to 2/3 of new prices these days.
I think it definitely depends, the firearms purchasing public is as diverse as most other groups.
As someone who collects both, I find it amusingly similar to camera gear. Nikon vs. Canon, Glock vs. Sig, 9mm vs .45 or was it APS-C vs. Full-Frame? In both cases there exists the mass-produced item most analogous to the "tree find". Glocks and DSLRs found at big box stores. Then there are collectibles such as Leica or something from the Springfield Custom shop, or Les Baer. I could go on.
At any rate, I think some things haven't changed, craftsmanship is still valued and prized, but the common purchase is definitely of the more affordable items such as the mentioned $600 price point.
Likely because partly what is considered a "good" handgun advances with the state of the art, partly modern insurance and regulatory requirements drive up modern manufacturing costs, and partly because of market dynamics for the use cases a handgun is put to. If you were mass manufacturing a mid-19th century handgun, with no improvements in its tech or metallurgy, without having to pay for the operational insurance and regulatory overhead costs, and it was accepted by the firearms-purchasing public in the same per capita adoption rates as back when it was originally produced, I can easily see it being a lot less expensive. But the purchasing public seems to seek specific characteristics in modern firearms, these characteristics don't appear to align with "use old tech", and this tends to set a floor price from what I can tell as a casual user.
Interestingly, replica mid- to late-19th century handguns sell for around the $600+ USD mark in the US, for the enthusiast market. Well-cared for, lightly-used firearms are reasonably close to quality as new for most non-enthusiast level users, and even many enthusiast users. So if inexpensive is what you are looking for, a used firearm from a trusted user goes for roughly half to 2/3 of new prices these days.