Tourist Cards are $10, Departure $10 also but...
Your airline, especially charter, may give you a tourist card with your boarding pass, if not you MAY be able to buy at the airport (though I have not seen that for a while with AA in Miami) and you can certainly get it at arrival before you go through immigration/passport control. Very easy to fill out, fill both parts.
Have a pen with you - there are little tables on pillars to complete the forms. On American you also have a customs declaration form they give on the plane (free) though on charters I have seen them not bother with that form for passengers.
There is a US$10 departure tax, in the case of American Airlines it is in the ticket, with others you may pay at check in or at a desk in the departure lounge.
Keep in mind many Canadian/US airports have such charges, sometimes in cash ( Vancouver BC) or in the ticket ( Toronto) though not usually on arrival, very often departure and all domestic flights, too.