NANDs are still produced in 14-15nm afaik. The only reason they got more capacity is 3d stacking but that has an obvious cost wall.

Your optimism about SSD prices is IMHO unjustified.

NANDs are afaik still produced in 14-15nm so the only way they get more capacity is stacking multiple layers.

So even if they add more and more layers the price of these NANDs will run into a price/capacity wall.

Have you actually checked if the drives are really dead and it’s not the SATA controller itself or other factors?