Presumably it's not just the cost of storage media, but storage of the media too. Climate-controlled warehouses leased in perpetuity, archivists, security, and so on. To be clear, I don't think this is why so much of TV and movies (not to mention radio) is lost, I think that's just lack of foresight or different priorities. My point is, I don't think just buying a few thousand off-the-shelf VHS blanks would have solved the problem.