"One way to get to Cuba as an American " a Cuba Travel Page by tomcarlson

we chose to fly through cancun, not only because tickets there (from nyc) were cheap, but cancun also seems to have the most flights to havana per day.
coming from the states, you'll likely land in terminal three. to head for cuba, you'll probably need to get to terminal two, which involves a shuttle. (there's an atm in both terminals, should you need mexican pesos). you can purchase cuba tickets from either mexicana or cubana. take mexicana if you can... cubana uses scary, OLD russian planes which run more like rollercoasters than jets. the ticket should cost around $260, plus two taxes (and airport and a departure tax, i believe), totally around $320. both airlines cost the same.

...and get them BEFORE you leave the u.s.!!! you'll get the best exchange rate with them, and the only place to grab them in cancun is from the american express desk.
REMEMBER: as an american, you CANNOT get money while you're in cuba. your atm card will not work. your american credit cards will not work. so, take more money than you think you'll need (you'll be spending it on more people than you think or want, possibly) with this in mind: cuba is not so cheap (for tourists) as you might think. there are plenty of cheap things there, but as a foreigner, you'll often be paying the foreign price.
also, save CUC 25 per person in cash for your departure tax from cuba!! even if you think the ticket you buy in mexico (or wherever) includes the departure tax, it does NOT.

upon returning to cancun, if you're stressed about having two mexican entrance stamps in your passport, the mexican customs agent will likely accept US $20/person. we tried to give our guy less, and he told us that we needed $20 each and then promptly stamped our passports! so, just stick a $20 in each passport and discretely guide the customs agent to the right page, asking if they could please not stamp your passport.
the double mexican entrance stamp is really nothing to stress about, though. their entrance stamp looks VERY similar to their departure stamp, so unless you have a customs agent heavily scrutinizing you, they'll never notice. especially if you have a bunch of other stamps in there.
JUST BE SURE to get rid of ALL cuba receipts and proofs of expenditure!!! you can bring things back with you... just tell them you bought them in cancun! (there are even cuban cigars for sale at the cancun airport, fyi). positively DO NOT list that you visited cuba on your american entrance form. it will most likely just add up to a few hours of uncomfortable searching at customs. REMEMBER: it's not illegal to go to cuba, it's just illegal to spend money there... but that doesn't mean you should mention it to uncle sam ;)