Originally Posted by
xliioper
It's generally not free (and not that cheap) on cheaper fares.
OK. But we do not know whether the OP will be traveling on a cheaper fare or a more expensive fare. We don't even know in which class of service he will be traveling, or who is paying for the ticket (the OP or a client/employer).
If the OP wants a true stopover, I would also price an open-jaw ticket, with a separate leg from NYC/MIA to Central America.