Wouldn't it be more like $0.07/GB for BDXL? If one got particularly lucky with HDD failure rates perhaps they'd survive running that long in RAID but one would expect some replacements over such a long period.

Some other things to consider are at high capacities all HDDs use helium now, which slowly leaks (WD/HGST have a SMART stat about the level*) and the cost of running drives/associated computers/maintenance over a long span vs the up front cost of passive writable media (edit: for some reason I assumed this was what was meant but they could be left cold which would likely increase survival odds and be cheaper).

* And there isn't much long term data about it that I could find, though some have reported between 1-5 years the SMART stat either remaining at max or dropping a few digits. Even Backblaze outside of their first article a year into using them hasn't seemingly continued reporting on the stat that I've noticed. I get the sense though that other types of failures are expected sooner than leaks.