I don't plan on running a public relay. I'll whitelist with my domain and certain pubkeys for my relay. I did think about applying for an open sats grant though. 

And if I ever get around to it, I would run a public relay with configurations for cost per kind event insertion. 1 sat per kind 1, 10 sats per kind 3, 0... Etc. using lightning or eCash to top up credit, right through the frontend.