I have a course that users are pre-enrolling on now, however I currently do not have a price attached to the course. Would I need to offer the people who have pre-enrolled for free or do I announce the price later on?
Users who are signing up for your course now whilst it's free will continue to have access once a price has been set. Only new users will have to pay for access. If you need existing students to pay, then you can expire their enrollments from your admin dashboard - they'll then need to sign up for the course and pay to continue having access.
Hope that helps!