Spirit is almost giving their seats away out of Fort Lauderdale to SJO.. If you can fly from FLL, become a member of the $9 FARE CLUB, and they send emails almost daily. The only problem is that you have about 24 hours to get one of the deals...
Check Spirit Air


You have a good chance of getting stranded with the smaller low cost carriers without many options, at least the big airlines can get you on another airlines flights out...a huge factor for me...

Tim- I know you are an experienced CR traveler but beware when you are coming back into to the US via Miami. My last three flights into the country via Miami ended with me being stuck there overnight due to the ineptness of AA. Make sure you have adequate time to clear customs and make your connection. AA is notorious for overselling flights and their ontime history is not the greatest when it comes to Miami.
I know all this info is probably not new to you but it may help someone else cashing in on the good deals. Wish I could take advantage of these deals but alas it will be March before I can venture back into the land of the Imperial Beer.

I have never had a issue in Miami or with AA in regards to missing the next flight, I always like a window of 2 hours between flights, just in case.
It also helps to know the holiday weekends thru Miami are a pain, so then I go through Dallas or Houston, which is less Caribe and Latin Flights...