I think the cheapest hard drives ever got to was around $10/TB for refurbished enterprise drives. So about $8,000 to store two copies of a 400 TB archive. It's a lot but not impossible for rich nerds to back up these collections. Making the content available to the world, with remote hosting, servers, etc. is what gets really expensive. And now storage prices are up because of AI.
The Library of Alexandria situation could be worse, but it could be a lot better. I want to see 100 TB - 1 PB holodiscs that cost $10 each, and a retvrn to 5.25" drive bays. Nuclear war is more likely at this point.