Pay for events

I'm looking to create a resource and events directory and would love to be able to have registered users:
(1) pay a one-off or subscription for the right to add an event in the directory
(2) pay a fee to add their event to the calendar
I don't really want to have a fixed fee (for say a 1 year membership) and then have them be able to add all the events they want, I'd like to have them "pay as you go".