from the cancun hotel zone, we took a R bus to the ADO bus center; there, we bought tickets (about $3/pp) to go to puerto morelos...the bus was extremely clean, comfortable, and very well conditioned. we were so impressed and the fare was so cheap ! the ADO bus will drop you off at the puerto morelos station very tiny infront of a pharmacy. from there you walk 50 feet to the corner and catch a cab for $2 usd to puerto morelos town (5 mins drive)
we took the cab to ceiba del mar hotel in puerto morelos because at the back of the hotel is a scuba/snorkel company called, ALMOST HEAVEN tours, and for about $38 or $40usd/pp we snorkeled for 2 hours with a guide who went in the water (2 reefs) with us. one of the reefs had tons of fishies but the other reef was mostly aquatic plant growth with very little to see.