I have used
Event Brite a few times, and they are easy to use. Here is what their site says about fees:
Eventbrite fees are applicable only for registrations or sales made online through the registration process for a non-free event. This includes if attendees use the Pay-by-Check, Invoice and Pay-at-the-Door payment methods.
Eventbrite does not charge any fees for the following:
1. Free or 0.00 tickets
2. When a discount code is used that brings the amount to 0.00
3. For attendees who are added manually by the event organizer