I usually buy from ServerPartDeals and goHardDrive. I missed out on a really great refurb sale of 12TB Seagate drives that were $74.99 each, but even now, you can find 12TB disks for $89.99.
My only problem with LTO5 tapes is the amount required to do backup. Were I going to do LTO, I'd have to go with LTO9 since they hold 18/45TB and are around $90 a tape.
I'm not sure how much write-protection would be useful in practice. If you're restoring from backups after a malware infection, you wouldn't directly restore on the infected system. You would first reinstall the OS/restore some earlier snapshot and then restore the data.
The point is you may not know a system is infected. There's more use cases for storing data on tape than only making backups. We clear data off spinning disks that we aren't actively working on. When we need it again, we get it from the tape. With a hard drive, you plug it in and the compromised system can infect the hard drive without you knowing. The malware doesn't have to actively destroy things for it to be a problem, it can take action at a later date, so with hard drives they can be a problem even when you don't know you've been compromised, and even after you've fixed the compromise if you've ever plugged in that hard drive while you were compromised. There is no write-protect on a hard drive that I know of. Tapes even come in "WORM" variety which is write-once, once you write data to the tape it can't be changed or erased.
Thanks for the explanation,I didn't consider this other use case. There are some ways of making a SATA connection read-only [0], but surely not as convenient as flipping a switch on a tape.
[0] https://www.nightofthedead.org/security/hardware-write-prote...
$74.99 for 12TB is still twice as expensive as the LTO 5 tapes I'm getting on ebay. The LTO drive was pretty cheap too, so I'm still way ahead in my 200TB archive with regards to price. The other thing I like about tape is that is has a physical write-protect notch, so if my systems were infected with some ransomware, it wouldn't be able to touch my tapes even if I have a tape in the drive. Plug a hard drive in and you could be instantly fucked by the ransomware.