If you make the event free it will attract a certain type of person.
If you make it one penny it will attract a noticeably different type.
A dollar.
Ten dollars.
A thousand dollars.
Different types of people.
Chances are you want to charge a ticket price where you make the most money possible while not irritating your audience and filling up the room.
But it’s also worth considering what type of person you want filling up the room.