Back in the day, my enterprise storage vendor warned us that tape was not terribly reliable and to no reuse tapes. The more consumer oriented formats were especially failure prone. Something like LTO was much more reliable but still not something you want to reuse a lot of times.
Hard disks don't have that problem.
So... you should probably compute TCO based on how your software vendor tells you you should use your tapes and not just gloss certain considerations over.