I am actually surprised at how well SSD prices have held their price. The technology has progressed, and drives now are faster, but on £ per TB it hasn't really moved too much - I bought a 1tb Crucial SSD for £120 about 8 years ago, and a similar equivalent today isn't much cheaper.Maybe i am misunderstanding your post but without a new interface i don't think external drives will ever be fast enough to run PS5 games.
Also you can buy NVME drives for the PS5 admittedly they are not available yet and will be expensive at first but as it is with new tech the price will come down.
I remember there was extensive flooding in Taiwan in 2011 and 2012, and that was blamed for HDD and SSD prices being so high, but it feels like the pricing has never recovered.......probably as they've realised people will still pay the high prices!