I have recently thought about burning some data to Blu-ray and therefore looked for some cheap blank discs. To my surprise, higher density Blu-rays seem to be much more expensive than lower density ones. In my country (Germany) for example, I could buy a 25 GB BD for 0,44€. A 100 GB BD would cost me 8,77€! At that price, it would be more efficient to store 100 GB on four 25 GB discs instead of one 100 GB disc (1,76€ vs. 8,77€). Sure, if it is one file I would have to split it first and combine it again when I want to access the data, but that effort seems to be worth it.
Why are high capacity Blu-rays so much more expensive, especially compared to HDDs or SSDs where the price per GB/TB usually drops with higher capacity?
To your first paragraph: Panasonic sadly stopped production this February (which is why around that time prices for all the remaining stock of their discs basically doubled). I’m still picking up some leftovers here and there. Sony I think is now only still producing the 128GB. All their 25 and 50 GB discs I’ve bought over the last two years or so were RITEK.BR3 and VERBAT.IMf.