Have a product option that adds a cost once but NOT affected by Quantity selector?

I run a music festival website that offers tickets to the festival with an option to pay for parking.

  • $50 per ticket
  • $5 for a parking spot

I have them as two products now, but of course people sometimes don’t realize there is an option to buy parking and just checkout with their tickets. I can’t simply add parking as a product option to the Ticket product because if the user is buying 4 tickets, and adds parking, the system charges $20 for parking because it multiplied the cost with the quantity of tickets - this is a problem if all 4 of those people just need 1 parking spot!

Here is my site Read-Only: Webflow - Black Bear Music Fest