Cruise.com via ShermansCruise offers a Carnival Cruise 4-Night Cozumel Cruise for two, with prices starting at $618. (On the ShermansCruise landing page, scroll to the bottom and click "Book Now" next to the May 10 sailing date.) That's the lowest price we could find for such a cruise in May by $180. This roundtrip cruise aboard the Carnival Fantasy departs from Mobile, AL, on May 10. Book this travel deal by March 31.