Do you really need a cloud, or can you migrate to one or more dedicated servers which - unless your project is small enough to fit on one of those $5 servers that only exists in clouds - are probably much cheaper than you think?
Yes, but do you need it? Hetzner will sell you a server with 4x16TB of raw storage (so, 48TB after you make it RAID-5, 32TB if RAID-6) for about $100/month. On S3, that's $736/month. $368, if we assume the server is only half full. If you have good backups and don't mind some possible downtime, use it without RAID and you are getting storage for 1/14 the price of AWS (not counting the backups).
Bandwidth is under a pretty generous "fair use policy" and if they decide you are not using fairly, overage is only $1/TB. On AWS, $90/TB and the free bandwidth is not very much.
Are you worried that you'll hit a huge traffic spike and need to upload 20TB faster than you can provision a new server?
If you really are set on cloud storage, B2 is cheaper than S3.
