Punchbowl does not currently offer a way for you to require your guests to pay for a ticket or an event fee before being able to RSVP to your event. We do offer the contribute
feature which allows you to collect donation for from event through your Pay Pal account. This is found in under the Invitation Options
Services like Brown Paper Tickets allow the collection of funds for ticketing. You can certainly use this service or another ticketing service in combination with Punchbowl. Just post your event ticket link
from the ticket service in the "Event Details" area of your invitation.