80GB of redundant storage = 160GB at least. More than that, because you can't count on any one node almost at all, so you need more than two copies.
This means you should get more like 10-20GB per 100GB you commit, otherwise the cloud simply will not have enough space.
Then if you consider that even with many nodes containing your data, there is a decent chance all of them go offline at a certain time. You have to have many, many nodes for the odds to be small enough. Which means the best solution is to use the storage you committed as one of the nodes, so it is always available to you. Then, it really transforms into a cloud backup system, rather than a cloud file system.