Heyas,
As the above poster said, the Tri-Rail is pretty cheap. 4 bucks I think. Go to their website and checkout the schedules
http://www.tri-rail.com/
There's also the Super Shuttle. I think it's $30 or so, and takes forever, depending on how many people have stops.
But here's the scoop on the train. The darn thing almost NEVER runs on time, and there is a whole bunch of track construction. On top of that, the shuttle from FLL to the station takes FOREVER, and the shuttle WON'T wait if the train is late.
The ride from the station to MIA is brief.
If I was commuting out of MIA, I'd get on the train in FLL 3 hours before of my flight, that was scheduled to get in 2:15 before my flight. I usually had to run to catch my flight.
Going the other way (MIA-FLL), the train is also almost always late, and as I said, the shuttle in FLL won't wait for a late train (even though all they do is the train station !!), so you're stuck at the station, with no cabs. It's about a 40 minute walk through a demilitarized zone to the employee lot if you're feeling lucky.
Nu