Try using a website such as Kayak.com or Yapta.com to "shop" and track your airfaire.
I'm going to Aruba in June and was able to get a flight from BTV (Vermont) on Jetblue for about $620 but fares have continually gone up since.
The great thing about Jetblue is that if you book your tickets but the price goes down, they will issue you a credit for the difference (which must be used within a year) with no deductible. I did this last fall on a trip to Orlando and got a $120 credit which I applied to my Aruba trip.
Sign up for Yapta's notifications for fare pricing and they will send you an email if the price goes below what you paid. The email also gives you instructions on how to get your refund.
Kayak and Yapta also have charts that predict the probability of the fare going up or down in the coming weeks (as well as show the history) in general terms for all airlines that fly to the destination.
Good luck!