Is nostr pay to play for content creators just starting out? 

Nostr is self hosted or pay. There is no real free infrastructure yet, although I wonder if ZBD has that kind of hosting capabilities.

What is the expected roi on paying to upload to incentivize that? 

Your content probably wont make much. There are a few documentary producers here nostr:npub1lelkh3hhxw9hdwlcpk6q9t0xt9f7yze0y0nxazvzqjmre3p98x3sthkvyz one who has had beautiful content but its not breaking even. I don’t think nostr:npub1lr2zzf989mvf393y0tv39ara6a4vddkd6y87z784up9vl6ks6j3qtudl6a is having a different experience.

But this is real early, we are still figuring it out as we go along.