Unless I misunderstood something, the comment you replied to has a link to HPE selling packs of 20 new LTO-6 cartridges (2.5TB x 20 = 50TB) for $60 (i.e. $3 per 2.5TB cartridge) which is far cheaper than a hard drive.

Correct, it also misses the core point of the discussion: SSD's and HDD's are unreliable cold storage long term. Cheap HDD's are better than Cheap SSD's (debatable if you're willing to spring for high end parts, but that's outside the scope of value/affordability), but if that data is truly important, it's well established best practice to replicate (be it cloning, mirroring, parity, what have you) your storage media.

Sometimes, unfortunately, a user will value the data more than they can afford to properly replicate/secure it it, and compromises must be made. Also, Tape does require a higher buy in than most (individual) SSD's/HDD's demand before you can even start investing in actual storage media, even if going used, so there are absolutely valid contexts where the "right"/best available approach is just throwing $200 at second HDD and cloning/mirroring it, but best available compromise in any given specific context is a separate discussion from general best practices or best value in broad terms.