As every vacation destination, in Cancun you can find different activities. While you lay down on the beach, people come and try to sell expedition to "Isla Mujeres", Aquatic Skiing, Trips to Xel-Ha and Cenotes, as well "parachute ride" on the beach. The prices range from USD$30-80 but if you negociate the prices and wait for the good sale, you can get cheap trips. Be careful and do not get rip-off sales people in Mexico. A personal recommendation is being careful with everybody you deal money, mostly all the people that work there are trying to make good business from the tourist, always ask for your change back, negotiate prices and be careful as well when going to the clubs directly with the staff from the hotels as usually they will charge more, and you even have to pay for the taxi cab back and forth. This is the negative part of going to Cancun, so instead of taxi, take public transportation, which cost $8.50 mexican pesos, or USD$0.70 and to see more the real Mexico.