We´re getting a little wiser as time goes by.
This time around I requested email ballots from the Polk County election board, which were dispatched within a couple of days. And again I will take them to the USA Consulate General in Rio where they will be returned via their daily mail pouch to the States -- free of charge (via the Citizen Services office).
The ballot comes with an envelope cover page that provides free postage. So once the mail pouch makes it back to Wash. DC, they just drop it into the regular postal service and it makes its way back to the Polk County election office.
This time around it will only cost me bus fare to submit both mine and Luiz´s ballots.
Since we are registered voters in Florida - our votes to re-elect President Obama are crucial.
Expats can get more information about voting from abroad at http://travel.state.gov/travel/living/overseas_voting/overseas_voting_4754.html