Yes indeed; if anything, they are understating the difficulties. This comes under the heading of ~exotic optical materials~. For example, we made these giant optical prisms for IR spectrometers, to exacting optical standards. The material was single crystal NaCl aka common table salt! Just imagine trying to grind and polish that, without being able to get even a single drop of water, your breath, or even slightly humid air in it, ever! After production, each and every prism assembly is stored in its own dedicated, desiccated, evacuated bell jar, under vacuum... and toted around like that. Breathe on it and you've just destroyed a $10K prism. Accordingly, exotics cost whatever it takes to manufacture and maintain them.
[I worked at B&L back when it was a full-service optical shop. Now they just make contact lenses and bottled water. There is precious little precision production in the USA anymore.] Tom