Lazy solution to an annoying problem
Ran into some limitations of unity, mainly that the .net version of the build I was using didn't support DriveInfo.GetDrives(). Since I had already written most of the game in c#, I didn't feel like starting over in a different language or engine, so I decided to go with a lazy solution.
I took the code I had written, made a new non-unity project, and created an executable that would calculate the current size of the drive, then just use System.Diagnostics.Process to run the application and read from its Standard Output. Though this made me make the game Windows only, as I didn't feel like figuring out cross-compilation.

Since I already had decided to make it windows, it meant that later I could call Process.Start("explorer.exe", "/select,\"" + _path+"\"") to open the file explorer with focus on a specific item, without having to figure out the equivalent for other operating systems (not to mention testing), so I guess it worked out.
Though in all honesty, the code I've written the previous two days has been pretty bad, and I never want to look at it again. I probably could have written it a bit more modular easily, not to mention there's code that would be pretty wasteful hadn't the project been this small.

Anyways, I'd love it if you would play my game, just don't look at my source: https://ldjam.com/events/ludum-dare/39/feed-me-your-files