I agree with the numbers, but I'd caution that they hide some possible costs. If you already have servers, server racks, power, networking infrastructure, regular backups, and software management to deal with growing storage amounts up to many TBs, then it's true that the incremental cost of another 1 TB is ~$100.
But if you have to start from nothing or closer to it (say just you and your laptop), then there's a rather large startup cost (plus ongoing local management costs) to get to the point where the marginal cost for the drive itself is the right number. In that case, since the cloud number is truly "all in", it might make more sense financially. It can also make more sense if you value your time highly versus the time required to manage the computational infrastructure in-house.
