How about "I imagined generating 70k audiobooks, and you can subscribe to my website for $50/month"?

You seem to be entirely focused on what the creator physically did and not what the user receives. They would not be available for users to listen to as audiobooks, if the creator only imagined generating the audiobooks

How about "just-in-time generation" of 70k audiobooks

It wouldn't fit into HN's characters limit

Thank you for support!