I us ITA's "On the fly" app. It sounds perfect for you as you are willing to travel from different airports. You can also go to the web sight,
http://matrix.itasoftware.com
but I prefer the app because I can set up my search parameters on my smart phone and check them quickly several times a day. It is crazy how much movement can happen in the matter of a couple of hours. On last years trip to SXM, I had checked prices in the morning, then at lunch they dropped $180 - so I booked . By dinner time, they had gone back up.

Here is the process I use:
1) In your mind, decide on what an acceptable price is.
2) Set up your search parameters and start checking several times a day. With the app on your smart phone it only takes a minute.
3) Don't be afraid to search and book by "one way" flight segments. There is very little discount for booking RT to SXM, many times your "down" segment" can be cheaper on one airline, and "return" segment cheaper on another. If you are taking a shuttle or limo to the airport, with multiple airport options, sometimes you can get a better deal by traveling out of one airport - and return to another.
4) If you can travel on "off peak days" you can save big bucks, especially in high demand times.

Good luck!