On-line Ticketing Services

Use a third party Event Ticketing service. This would be an end to end solution: set class/event size, record list of participants, collect payments, manage refunds.

Here are a few used by some local Boulder people. These have no monthly fee, but collect as % on each sale.

Brown Paper Tickets
https://www.brownpapertickets.com/
Ticket buyers pay just $1.49 + 6%, which includes delivery and credit card processing.

Example:
https://www.brownpapertickets.com/event/6633185?ref=349591

Humanitix
https://humanitix.com/us/for-hosts

Humanitix is completely free for event hosts with no setup fees, monthly subscriptions, or pricing tiers.
(there is a processing fee)

Example:
https://events.humanitix.com/september-24-etown-radio-taping-ruthie-foster

This one is the most popular:
Event Brite – most popular ticketing app
https://www.eventbrite.com/organizer/pricing/
No fees for free events
3.7% + $1.79 service fee per ticket
2.9% payment processing fee per order
Example:
https://www.eventbrite.com/e/holly-black-with-paolo-bacigalupi-live-at-tattered-cover-colfax-tickets-1425591876679?aff=ebdssbdestsearch