Back of the napkin, a week at Sandals Nassau for two is about $5k give or take for September next year, plus airfare.
Just the room on the Carnival Liberty out of NOLA is about $4k. Plus airfare, plus air transfers, plus elevated food and drink, plus excursions, plus gratuities.
Granted the cruise goes to Nassau, Freeport, and Key West. At Sandals you're in Nassau for the week, but with all your excursions etc included that's not so bad.
Cruises are not cheaper than AIs anymore folks...