Hey @Michael!
While the automatic date-switching and stuff is a bit complex for the scope of these forums, you can pull off the basics of just displaying a different “Early Bird” cost using Events Calendar Pro’s “Additional Fields” features.
You can learn about these fields and how to use them here → https://theeventscalendar.com/knowledgebase/pro-additional-fields/
Now, if you need more control over the fields or where to display them or anything like that, then unfortunately you can only do that with custom code 🙁 We are not able to help with custom code here, but you can get started by learning how to store and display custom fields information on Codex articles like this one: https://developer.wordpress.org/reference/functions/get_post_meta/
I hope this information helps!
Cheers,
George