With 1TB of object storage costing as little as $6, I believe that most sites who are heavy on uploads aren’t much worried about storage costs nowadays. When paired with our Client side image optimization enabled by default, it means that it costs you $6 per month for every ~2,000,000 pictures uploaded by users.
That said, I hear you on users abusing PMs, that is a problem I had to fight in the instance I was the main administrator. In the end I almost disabled PMs to discourage it’s use by making the limits very low on all PMs settings.