If you set your object store to be resilient to single-partition loss per object (within CAP) you effectively duplicate everything once. If you want more-than-one you get into sharding to spread the risk. We're not talking about RAID here, but about replicas or copies.
Windows Storage Server doesn't belong in a setup like this, and neither does tape since it needs to be accessible in under 1s. If higher latencies were fine the author would have been able to use something between S3 IA and Glacier. Heck, you could use cold HDD storage for that kind of access. The drives would need to spin up to collect the shards to assemble at least one replica to be able to read the file, but that's still multiple orders of magnitude faster than tape.
I have written a larger post with more numbers, and unless you seriously reduce the features you use, it's not really cheaper than S3 if you start off with no physical IT and no people to support it. It's not that it isn't possible, it's just that you need to spin up an entire business unit for it and at that point you're eating way more cost.
Regardless of the object store (or filesystem if you want to go full on legacy style), you still need at least the minimum amount of physical bits on disk to be able to store the data. And pretty much no object store supports a 1:1 logical-physical storage scale. It's almost always at least 1:1.66 in degraded mode or 1:2 in minimum operational mode.
