We went there with our car, from Merida (ca. 1.5 - 2 hours). Celestun and Falmingo/Mangroves really deserve a visit! The Flamingo/Mangroves's tour is really excellent and a perfect change after days with maya ruins: for ca. 100.- USD (per boat, not person) you will have a 1.5 hour's boat tour and what you'll see it's spectacular!