So, here is how I've always done it.
Start a group PM with everyone who wanted to go.
Give them a deadline for them to send you the money over for the ticket, along with the number of ticket, camping passes, car passes (1 car pass per person).
Total amount is cost of tickets, plus price of recorded deliver, plus PayPal fee (as I always did it as a payment to give assurance incase something went wrong).
At deadline, order the tickets. If you have more tickets ordered than car passes, make up the difference for the number of car passes (order the same number, as I can guarantee someone else will want to come at a later date, so they'll need to purchase their own ticket, but you can then send them a stand pass).
Once you have the tickets (usually 2 weeks before), post them out, and let everyone know their recorded delivery reference.