This article has a number of things that are basically true but one has to discount everything by 50% for the particular company advocacy, ie GREATEST OPTICAL MANUFACTURER EVER puffery. This is not to criticize your conclusions, merely the biases of the article.
Most optical glass manufacturers are capable of making a wide array of glasses to suit lens designs for all but the most exotic lenses (excluding aspheric and molded/machined designs which are another realm of manufacturing difficulties). One cool thing is that Ohara gives us mortals a rough idea of what each of their glasses costs. Have a look at their chart:
https://www.oharacorp.com/pdf/pricing-chart-2018-01.pdf They only give rough price ranges and production frequencies, to get real numbers one needs to request a quote. Nevertheless, they have nice price ranges relative to S-BSL7, which is the Ohara borosilicate crown glass equivalent to Schott's N-BK7. This is basically the lowest cost optical glass, so if you order a random lens or window from Edmund Scientific, it's usually made out of N-BK7 or the equivalent. Ohara says it cost ~ $10/lb in 2018.
The high-index rare earth glasses that we identified from the Nikon patent were lanthanide crowns with say index n ~ 1.7 and Abbe number ~ 50-60. From the Ohara chart color coding, these are mostly in the "medium" price range of 3.5-6 times the borosilicate crown, although there are a few that are higher. It's possible that in 1970 when these glasses were more recently developed that the difference was greater.
The small elements of a wide angle lens probably each weigh less than a ounce, although I'd guess each began as a blank that weighed maybe twice as much? So at today's prices, the bulk glass for each element in an ordinary lens might cost from $1 up to ~ $5 for a rare earth element as a
very rough estimate. Certainly for mass production the price of the glass is a factor restricting the use of expensive glasses, but the fabrication and assembly costs probably count more than just the raw material cost.
Once you get to really large elements or flourides such as CaF2 or BaF2, all bets are off. There, the difficulties of casting and fabricating can be much greater and the glass really is a significant engineering problem.