If you’re using eventbrite you can set up conversion tracking pixels for most ad platforms on your manage dashboard. Screen grab below:
Are you using pixels? You really need to be using pixels to get the most out of ppc, otherwise, as you say, you’ve no idea how much you’re spending per conversion. Pixels will give you this data.
I actually think sending people straight to the ticketing page is a good idea, as long as you have a well filled out event page and description with enough info that people can make a decision. It cuts down the number of steps a customer has to purchase a ticket, and therefore can increase your conversion rate.
If my event ticket price is not high e.g below £20 i’d probably send straight to event page. If i was doing a conference or festival with a much higher ticket price, this may not work as well as people need more time to digest info about the event before they are convinced. In this case i’d direct people to my website where they can read all the great content about my event, watch the video etc and get interested, and then i’d retarget them and send them to the ticket page.