$35.00 tourist boat in the hotel zone or take the peoples boat at Cancun ( newer boat ) or Puerto Juarez. Catch the public bus R-1 or R-2 at the hotel zone. It will say on the window Puerto Cancun or Juarez. Let the driver know and stay near the front if possible. You can see the big blue port tower from a good distance. You then buy a tcket, get on the boat with AC and touring bus type seats & go $7.00 round trip in 1/2 the time, giving you more time to explore the island.
Wow, I was a little taken aback by the 'hard sell' atmosphere on Av Hidalgo and by the big resorts trying to get you into a timeshare presentation. We were in Isla Mujeres in May/June (low season) and we were still pestered, mostly by time share front men.
Kind of a double edge sword as I know that these guys are just trying to make a living, but it got a little old after a while and we would plan our walks to avoid known "hot spots".