There is a bus station at Juarez and 5ta. Avenida.  The air conditioned buses to the airport leave every hour.  The cost is 80 pesos, about $7.50, per person.  It takes about one hour from Playa to Cancun Airport, and they leave you right at the front door.  You can buy tickets there or online at  www.ticketbus.com.mx. You can even choose your seatting online.