USB drives aren't that expensive. Why not just grab one of those.
I'm not sure that optical disks will be obsolete any time soon - niche, but not obsolete.
I have about 8TB of media (mostly TV/Film caps and suchlike) that I want to back up permanently and store long-term off site in case my RAID array fails.I add 1-2TB to that each year. 50GB Blu-Rays (or possbly 25GB ones which seem cheaper and safer long-term) are looking like the bast option, given the expense of tape drives.
Burning 150-160 disks one-off over a few months, then 20-40 disks a year doesn't seem like a great hardship. Certainly it seems to stack up well against the alternatives. $50-$80 per TB also isn't outrageous. Certainly, I don't want to ever have to restore all the disks and hope never to have to, but at least I have the option with a backup.
And I still buy the odd film on Blu Ray - quality is *much* better than streaming.