Example: Rolex Daytona in steel retails for ~$13,000. You can buy that from the store and immediately sell it on the secondary market for $30,000+. The Patel Phillippe Nautilus 5711A is similar ($25-30,000 retail, $75,000+ secondary).
As it happens when the current Rolex Daytona came out a few years ago the market wasn't anywhere near as hot and the market was flooded with people flipping the old model for the new. I happened to buy one of the old Daytonas for $10,000. Last time I checked it sells on the secondary market for $35,000. It's nuts.
For anyone who is interested in this, the plae I would start is with only these two brands: Rolex (first) and Patel Phillippe (second). They completely dominate any sort of demand and have a healthy secondary market. With vintage watches you get into all sorts of weird preferences that make massive differences in value and some of those details can be pretty minor (eg rail dials [1]). Some go for astronomical prices, most notably the Paul Newman Daytonas [2], which are funny because when they were production watches they typically sat on shelves for years because no one wanted them.
It's a fascinating world because what you discover is that Rolex are absolute masters of brand management. Like they are absolutely second to none. Omega, for example, produces some high quality watches, sometimes much better than the Rolex equivalent from a pure utility POV (eg Planet Ocean over DSSD). But Omega produces too many watches and too many models. Rolex quite famously has very limited product lines, which is fantastic for a secondary market. Rolex watches really are almost as liquid as cash.
The other interesting thing is you get into the pedigree and history of each of these watches. For example, GMT watches came about in the 1960s to solve a need as pilots started crossing time zones. The Daytona was for race car drivers. Submariners were (and are) for divers. Sure they'r emore of a fashion item now but the history is fascinating.
[1]: https://www.bobswatches.com/rolex-blog/resources/rolex-rail-...