We moved to AWS a few years ago, after self-hosting our own storage for years. What a nightmare.. The egress fees were killing us, so we had to find something else. Being weary of these large tech companies, and being that these days we're more privacy conscious as well. We found a new startup that outsources storage nodes to individuals / businesses.
You have to install what they call a "relayer" on prem. The relayer is the S3 endpoint. It breaks up the data and encrypts it before sending each piece to a different node on the network. No centralized behemoth holding us hostage over our data and no egress fees. We're a smaller company, so I was able to talk them into trying it out. I doubt you'd be able to talk an enterprise into using a lesser-known technology though.