Tulum: the list

Hotels
Posada Luna Del Sur, hotel in Tulum pueblo (rooms from 800 pesos)
Hotel Posada Lamar, hotel on Tulum playa (rooms from 1200 pesos)

Do
Tulum ruins (entrance fee: 51 pesos)
Tulum beach
Learn to kiteboard with Extreme Control

Eating
El Camello Jr, south end of the Tulum pueblo stretch (roadside seafood restaurant serving guacamole: 30 pesos, ceviche: 50 pesos, fish: 70 pesos)
Habanero, north end of Tulum pueblo (cafe serving simple breakfasts, good comida corrida, good jugo naranja)
Antojitos La Chiapaneca, south end of the Tulum pueblo stretch (taco joint serving tacos al pastor, 7 pesos each)
El Asadero, Satelite Norte - west of the north end of the Tulum pueblo stretch (Mexican grill serving Angus beef, chorizo, roast potatoes and onions, grilled veges including chilies and cactus)

Get around
Cabs to the beach shouldn't be more than 50 pesos. A great option is to rent a bike (some of the cheaper places to stay in town include a bike in their room rate) and ride the bike path to the beach each day.
Buses direct from Tulum to Cancun airport are approx 200 pesos. Cabs are around 600, but from the airport, they tend to charge more like 1000.