Cruises Only offers a Carnival Cruise 4-Night Caribbean Cruise for Two bundled with a $25 onboard credit with prices starting at $338. That's the second-lowest price we've seen for a 4-night Caribbean cruise, and assuming you use the credit, it's the lowest current rate we could find for this cruise by $25. This roundtrip cruise departs from Miami, FL, on April 22 with stops in Key West, FL, and Cozumel, Mexico. Additional taxes and fees may apply. Deal ends April 12.