The cheapest and most convenient way of travelling throughout the Hotel Zone is by taking a bus. It can also be a lot of fun. Cancún public buses are known for impromptu sing-songs, especially if someone brings a guitar along. They are also the quickest means of travel for musicians and DJs, on their way to entertain the crowds, and many seem to start early. Film sharing sites, like You Tube, are filled with shaky tourist footage of vibrant Cancún bus journeys. Happy, smiley faces abound; voices raised in song; guitars and makeshift instruments leading the way; all on a public bus.
Here's just one example, taken at night, presumably en route to or from one of the nightclubs:
The buses on the ocean side of the boulevard are heading towards downtown; those on the lagoon side are heading towards the airport. Both of them will make regular stops along the way. The rate is $6 pesos (60 US cents).
The Hoteles R1 buses go in a huge circle through the hotel zone, along Avenue Tulum and back to the bus station (crucedo). Therefore, buses run up and down Boulevard Kukalcan every few minutes. The R2 and R15 buses will go downtown, including a stop near to the local Wal-Mart.
They can only stop at the designated bus stops (parada). These are signposted along the boulevard as a blue square with a white picture of a bus on it. However, they won't necessarily stop unless you ask them to. If waiting at the stop, then stick out your hand. If sitting on the bus, then call out 'stop' or pull on the cord. Again, they can only stop at the designated bus stops.
During the day, these buses can be very crowded, so you may have to stand up. During the night, when most passengers are intoxicated and in high spirits, they can seem like a mobile party.
R1 - Take this route to go downtown, or to Puerto Juarez, Wal-Mart, Plaza 2000, Mercado 23 and the Cancún bus station.
R2 - Goes to Wal-Mart & Mercado 28.
R15 - Goes to Wal-Mart & Mercado 28.
R27 - Goes along Tulum Ave to Plaza Las Americas where you catch the collectivo to Playa del Carmen and Tulum.
There is an interactive map of the bus stops along the Hotel Zone here.
For those wishing to go further afield, then you will need to go to the bus station (crucedo) and purchase tickets. These will reserve your seat. There's no real difference between first and second class buses other than the fact that the former will reserve seats. There are also luxury buses available to go to places like Merida or even Mexico City. The longest single journey you can make on a bus is to Mexico City and takes 26 hours.
Ticket Bus has a list of all of the prices for long-distance trips via bus.