You may have an advantage in that you are somewhat close to Charlotte and can get a direct flight to SXM. If you don't care if you have to take separate planes or that you may not get seats together, you may find a great deal closer to the departure date since prices are lowered to fill planes.

We just booked for March direct BOS SXM for $729 rt which is the lowest we've ever paid for early booking and the plane was already 2/3 full. Now the price has risen greatly.

It's always a gamble. Gas is purchased ahead so prices won't affect fares for awhile. You have to decide what you're willing to pay then book. YAPTA.com will monitor prices for you and notify you. When you feel it's good for you, book.