I imagine there would be a blanket amount that covers small creators. Something like $200,000. Now if a movie studio claimed that a new movie costs $150 million to produce then they’d would have to show the accounting for that. If they could then they would be entitled to maybe $225 million ($150 million + 50%) before the movie goes into public domain.
Big businesses already have figures about what a creator’s time and effort is. For small creators there would be some fixed amount, like $200,000 or something, that they’d be entitled do just by creating something. If they claim their expenses were higher than that then they would have to produce receipts.
I have to imagine that a number like $200,000 for writing a book or song is pretty good. Stephen King has written like 65 books. At $200k a pop that is $13 million just from book sales. That’s not including public appearances or speeches and stuff that could also earn money from the fame. That’s rich, but not stupid rich. Mr. King’s net worth now is like $500 million or something.