- Paying for physical space and facilities
- Paying people to maintain it
- Paying for DRP/BCP
- Paying periodically since it doesn't last forever so it'll need replacements
But if you were to have to move out of AWS but Azure and GCP aren't options, you can do: Ceph and HDDs. Dual copies of files so you have to lose three drives for any specific file to have (only those files) dataloss. Does not come with versioning or full IAM-style access control or webservers for static files (which you get 'for free' with S3).
HDDs don't need to be in servers, they can be in drive racks, connected with SAS or iSCSI to servers. This means you only need a few nodes to control many harddisks.