You must pre-pay at the airport and receive a voucher. You can get a private cab for $60 (and yes, they quote the price in dollars and not in pesos) or a shared ride for $16 per person. Then you wait ... and wait ... and wait. The lines are disorganized; the system susceptible to having people jump in line if they have found the right person to tip. Which is something you might consider, if you don't want to wait at least 30 minutes in the hot sun. I was only starting to figure out the system right before we finally got our cab (chalk it up to being up since 3:30 that morning), but you should check for the color of the shirts the guys are wearing. The white-shirt people sell the vouchers. The yellow-shirt people communicate with the cabs and vans, and designate who gets loaded in. Unfortunately, the guy who seemed to have the final say as to who got loaded next, also had a yellow shirt, so you will need to scan amongst the 'yellows' to see who the others are deferring to.
There does not appear to be any way around the system. They have it locked down, and as a result the number of available cabs have gone down (fewer are willing to pay the overhead to voucher system company) and the price has gone up substantially.
Given what we ended up paying to take a cab to our hotel in town for an overnight stay, and then the cab down to Playa del Carmen to take the ferry to Cozumel, it would have cost us less to reserve a rental car for a 24 hour period (Note: rental cars from the mainland are not allowed to travel to Cozumel). The car rental is easier because the rental company van shuttles you over to the rental office at the airport.
Live and learn ....
