What about backblaze b2 with rclone, I'm sure there's a front end somewhere and with the clousflare cdn it's no egress cost. Or clousflares storage amounts
I've made one such frontend for not only backblaze but also Nextcloud (via webdav), and pretty much every protocol like FTP, SFTP, S3, ... It's all open source: https://github.com/mickael-kerjean/filestash