https://www.usa.canon.com/shop/p/rf1200mm-f8-l-is-usm-lens
but the f5.6 version... doesn't seem to be:
https://www.the-digital-picture.com/Reviews/Canon-EF-1200mm-...
"Minimum focus distance of Approx. 14.1 ft. / 4.3 m. "
Which is conveniently able to be measured by taking the distance from the camera mount to the end of the lens, then doubling it! However, at least this is "affordable" enough to have a price listed. The Leica lenses I was referring to has the "oh boy, this is going to be expensive" infamous Find a Dealer button. Also, it's a set of 11 lenses, and for nearly double the price, they add in a few more wide angles and a few more telephoto lenses to the kit.
A real answer to this would be to break it down by materials vs labor. Not shaming them for being curious and then saying it's high end.
So unless you can tell me that you've hand ground a telescope mirror of any size to have direct knowledge of the experience, I'd suggest taking a look at the process while considering the size of the mirror discussed. Even the base and the trusses for the assembly will have required design time and iterating through changes. Not sure why this seems so strange compared to all of the other things in life with "accepted" price tags.