Backblaze B2's calculator is a little more sophisticated, and putting in the numbers for an absolutely pathological usecase where you start with 4TB, download, delete and upload that same amount every month puts you at $720/year. A much less pathological use case (I think) that assumes you upload, delete and download 1TB/month puts out around $360/year.
Hetzner storage boxes offer 10TB for ~$48/month, which is $576 a year -- free ingress/egress, no hidden fees for operations or whatever else, but you do have to set up a node with minio (or use FTP, etc).
Amortized over the happy time (time where you don't need to rely on your backups) this does make sense, but I wonder what the percentages look like on that kind of metric. To be fair I haven't had to restore from backup for years so this probably makes a lot of sense. I guess there's no need to test your backups/restore either if you're using a tool like borg/restic/etc and have tested it with local hardware.
Also, what happens if you have to retrieve data twice from Glacier? You've got access to it for 24 hours so I assume you're planning on just keeping the data on some non-glacier storage medium for a while after the initial post-disaster pull?