This kind (bakelite - black one) can still be found in some buildings built in 1950's or 1960's.

I wanted one (not so much for retro purposes but to prevent turning off the light accidentally at a place) but the prices are outrageous - like 10 times to 30 times more expensive to a good quality normal light switch of the same type! Just because it's retro? Yes, the rotary mechanism is more complicated but if the price was 2 or 3 times more, I wouldn't tell a word. Not that I couldn't afford buying one, but I really don't wan't to pay for a fancy thing and will think of making a shield to prevent those accidental switchings.

The #2 is made of duroplast and I like it's shape best. #3 and #4 are ceramic - not really needed.

Beside being a "retro-novelty" (which adds a premium), it just is not the mainstream, so no economy of scale.

And the original old designs are unusable, because they were build around materials and construction style which are not acceptable anymore (safety, ROHS,...), so we are talking about newely developed mechanisms that needed to pass all the required certification tests and someone has to pay for all that. And when the production volume is limited, it just translates into rather high unity cost. That is just a fact of life.

If you don't care that much about the asthetic (when you e.g. may cover it into some installation box,..), you would be better "fishing" in industrial control components "waters". I would even guess that would be where the internal mechanism even came from, by the way - rotary switches are still quite common, exactly for the reason you are describing...

I have a little stash of these old things. But they're surface mounted ones, not built-in ones. Haven't decided yet what i'm gonna use them for.

The actual bakelite or melamine switches, outlets and such are usually not more than 30 euro afaik. Fairly reasonable for a highly specialized part, if you don't need dozens of them.