All the signing up is done online. I think you can technically sign up until the day of the event online, but the people running the sign in table may have the latest list of attendees that was printed 1-2 days before. Just have your printed receipt and you will have proof you paid online. Otherwise you can pay in person at the event. It just helps the instructors decide how many need to attend, based on the numbers that have preregistered. Since it is all volunteer, it is nice to know these numbers as far in advance as possible, but we usually see a majority of the attendees sign up in the two weeks before the event.