Ooops, correction, it's €3.99 for 100GB and €19.99 for 1TB, doesn't show you that until you tick the option on the config page. The Unlimited part is just for bandwidth.
OK, So Wasabi still seems cheaper on the backups, with Hetzner Storage Boxes sometimes less if you'd be adding and deleting a lot of files on Wasabi.
In this case, I don't know another need for FTP backups, so defer to others if anyone knows other options, perhaps home-servers with it.