* Kubernetes
* High-level storage services: Ceph, Cassandra, NFS
* Lower-level storage for whatever you pick for the previous point
Each of those, and the combined service you build, needs staffing for operations, monitoring, security, etc. support. If you follow any security standards or are in a regulated industry, you're on the hook for documenting compliance on all of those, too, especially if you need to be able to demonstrate things like immutability.
You certainly can do this but that's a number of full-time jobs requiring expertise. If you have enough storage usage you can potentially justify the savings over the rates you'd be able to negotiate but that's a big up-front cost which you hope but are not guaranteed to recoup.