I wonder just how "expensive" they were for the times? They were just razors after all. I'm sure they weren't something that everyone had but was that because they were relatively expensive for the times or just something that most people weren't that interested in?

Just like today even among the wet shaving community. Some people have lots of razors or soaps or brushes. Other's have fewer items but it's not really because they can't afford to have more.

I do think, as was mentioned above, that they seem pretty convenient given how long you could go between maintenance honing.