Lenses today tend to be polycarbonate plastic anyway - which means they can be produced rapidly like any other plastic moulding.
Both SLA and FDM 3D printers are now able to make curved surfaces with 10's of micrometer precision across the lens surface, and local 10's of nanometer smoothness (usually via a surface-tension based smoothing process).
Usually you then use that as part of a two part mould to make the lens out of polycarbonate or some resin which has optical and hardness properties you want.
The whole lot, if done in ~10M quantities should come out to only 10 cents or so per piece (with each piece having a custom geometry).
There are really big opportunities available for doing this to contact lenses, since the lens can then fully compensate for any unevenness in the eye below, and could possibly lead to superhuman vision if done right. The same can't be done for glasses since the eyeball moves - instead the best you can do is a best-fit approximation for looking ahead.
I have noticed that in France glasses with decent but standard frames cost around 5 times as much as in the UK. My suspicion is that the difference is related to how supplementary health insurance works in France rather than any special manufacturing requirements.
The amount of prism is now to the point that adding more is not really possible and thus if it gets worse next step is surgery on the muscles controlling the eyes or intentionally letting one eye look away. Over time the brain starts to ignore the other eye for focused vision (it would still get used for peripheral vision)
But yeah without the prism the lenses are like 30€. Once you add prisms the lenses are around 350€.
I have a severe case of Strabismus (Exotropia) and my left lens requires a prism in order to keep my eyes focused on the same target. The required prism has gotten strong over the years and as it has, the price of the prism has gone up as well. The prism alone added nearly $200 to my lens cost this time around.
All that said, I imagine the lack of competition (the thread topic) is at least partly to blame for this. I highly doubt my glasses cost anywhere near that much, even if they are special.
