This is high season, so certainly not the cheapest time to go.
I have a trip down to Aruba scheduled soon. The flight from Baltimore cost me $239/person one-way (hitting Cartagena before returning) and I booked accommodations through airbnb for $70/night (small one bedroom cottage). This doesn't include car rental or food & drink, of course.
Not saying you have to go the airbnb route, as it's not for everyone. But, maybe look beyond an all-inclusive?
Mike...