I would buy commodity hardware and build my own storage cluster with ZFS and just put Minio in Distributed mode on it. You have full control of redundancy level

I would buy commodity hardware and build my own storage cluster with ZFS and just put Minio in Distributed mode on it. You have full control of redundancy levels either on the cluster on individual ZFS pool side and can fine-tune what your business needs. Maybe you don't need to mirror all the data so you can have RAIDZ2 with just 20-30% extra cost. Hiring staff to build this would make sense at this point, because if your S3 storage cost is really $200,000/month, you can hire 3 good engineers with $450,000/year, which is the cost of just two months of S3 storage.