As an example, on JetBlue, I found seats departing JFK on Wednesday, August 28, and returning from AUA on Thursday, September 5, 2019.
Fares from JFK are available at this price starting on select dates in May and June then again in late August with departures valid through early December, returns in late December possible. Departing from Boston fares are mostly available in late August and September, with the occasional random itinerary in springtime.
You'll need to be flexible with your travel window to find dates that work, but your best bet is searching in September and early December. JetBlue's inventory is selling out quickly, so on most dates, you'll find these fares operated on Delta. From Boston, JetBlue is the only choice for a nonstop flight on this route at this price.
These fares only include one small personal item and one standard piece of carry-on baggage. Checked bag fees start at $30 each way.
On Delta's Basic Economy fare, seats will be assigned at random upon check-in for this price. Jetblue's fare includes standard advanced seat selection.
Delta's Main Cabin Economy fare is $50 more roundtrip, which comes to $417. This will include advanced seat assignments and allows ticket changes/upgrades for a fee. A checked bag costs the same $30 each way.
JetBlue's Blue Plus Fare is $56 more roundtrip, which comes to $423. This will include one piece of checked luggage, which is the cheaper option than paying for baggage at the airport.
Looking for a place to stay in Aruba? Hotelwatchdog will get you started with this list of available accommodation for the sample dates mentioned.