This is probably too cheap, but Blu-Ray media is about $2/25GB, or $80/TB (and a new standard is coming). You'll want a lot of redundancy, so "just" $40k in med

This is probably too cheap, but Blu-Ray media is about $2/25GB, or $80/TB (and a new standard is coming). You'll want a lot of redundancy, so "just" $40k in media won't get you there, but it is less than the $120k for hard disk storage quoted by pstack (Blu-Ray discs don't even need power and cooling; on the other hand, Backblaze Pods don't need interns to keep feeding them blank media). You should probably do some RAID-like error correction to keep the number of extra copies you need reasonable. (E.g. two copies of every disc, every fifth disc is just the XOR of the previous four; that'd give you two backups for every disk at a total cost of $90k.)