Hi,
Thanks for using our plugins. I can try to help out here, but I am limited in supporting customizations.
A good place to start with any customizations is our themer’s guide:
https://theeventscalendar.com/knowledgebase/themers-guide/
The two files needs to change the tooltip are:
plugins/the-events-calendar/src/views/month/single-event.php
plugins/the-events-calendar/src/views/month/tooltip.php
And this function will return the price:
tribe_get_cost()
Please review that and I can help if you get stuck, but might not be able to provide everything.
Thanks