Hi seattleshakespeare,
Thanks for getting in touch and for your interest. Events Calendar PRO does not come with a built in purchase button type feature. However, with both The Events Calendar core and with PRO, you can always embed a button or link in the event description to take the user to a third party ticketing service.
The main reason I could see you opting for PRO is because you could put the link in as a Additional Field with the other event data. You can learn more about adding Additional Fields here.
Does that help answer your question?
Best,
Leah