Haven't done that trip from El Cid. But it is easy to take collectivo (8 Pesos) to the 307 then take the Ado (can't remember exactly...maybe 40 Pesos) to Cancun Centro then take taxi (80) Pesos to Puerto Juarez and get on the Ferry. Sorry don't remember the cost of the Ferry...I seem to think it was around 300 Pesos. This is an easy trip.
Post #1 is exactly right. :)
Ferry is $300 for foreigners