I'm glad you're focused on a sustainable business model, but try to connect cost with value. If I sell an album on your site for $1000 or $10, it doesn't cost you any extra but my fees are 100x.

If hosting is an issue, create monthly plans based on usage or additional features. That's your value, that's where the business cost is, so that's what users are paying for. You aren't a payments company, so don't make your money on payments.