How could that be true? Good flywheels are kept in a vacuum, on magnetic bearings. I came across one that uses high temperature superconductor. Often, they're strengthened with carbon fiber (but why would that affect cost efficicacy? Why not just make a larger number of cheaper ones without the strengthening that can't spin as fast?).
I still can't believe this and I suspect it comes down to economies of scale or something annoying like that.
Merveilles is a community project aimed at the establishment of new ways of speaking, seeing and organizing information — A culture that seeks augmentation through the arts of engineering and design. A warm welcome to any like-minded people who feel these ideals resonate with them.