From Miami, a relatively inexpensive full-fare coach trip is the following:
MIA-CCS on Aeropostal
CCS-BOG on Avianca
BOG-PTY on Copa
PTY-SJO on Taca
SJO-MGA on Lacsa
MGA-MIA on Lacsa or Taca
With CCS-BOG-PTY-SJO on one ticket, I've had this priced at < $1050.
The biggest downside is inflexibility on some of the routes. There's only 1 flight/day on the specified airlines from BOG-PTY and PTY-SJO. This seems to force you to spend a night in Bogata.