There are at least these 3 flights from cities in the USA to Cozumel:

American Airlines –  Dallas Fort Worth – Cozumel  Direct flight at 10:55 AM.
Continental – Houston – Cozumel Direct flights at 9:10 and 12:15  (2:17 hrs flight).
Delta – Atlanta – Cozumel Direct flight at 11:15 (2:32 hrs flight).

On arrival to the airport, take a taxi (15-20 min) to Fiesta Americana. The prize should be about 10 USD.

To Cancun there must be more, even from Europe.

On arrival to Cancun, there are buses that go to PLAYA DEL CARMEN (the bus line is called ADO,

and it is just going out of the airport, prize about 8 USD). Go to the indicated lane (I believe it is No. 56). The trip takes about one hour.

On arrival in Playa del Carmen, go out of the bus station, cross a little garden, and take the ferry to Cozumel

(this takes about 45 min, prize about 11 USD). Then take a taxi (~15 min) to Fiesta Americana. The prize should be about 8 USD.

Any doubts, contact hmmc@inaoep.mx.