Carnival offers 4-8 day Caribbean cruises starting under $300 USD.
These quotes are per person and double occupancy. As these cruises fill, expect the minimum price to go higher until the end of the promotion. Expect to see deals like this come and go--don't be surprised when they disappear quickly. If you like the deal and you're ready to book it, don't wait.
Norwegian Cruise Line has a specials page that recently offered a five-day western Caribbean trip starting at $299. This itinerary includes Roatan, Honduras, and Grand Cayman from Miami. It's the kind of bargain that won't be around very long, as the disclaimer implies: "These offers are capacity controlled and may be changed or withdrawn without notice."
It's a little off-topic, but NCL also offers a five-day Pacific repo cruise starting at $299. Don't expect many ports-of-call, but at $60/day, can you really complain? Check out their selection of repo cruises and realize that there are groups of experienced cruisers who are waiting to click "reserve." If you want one, don't wait long.
A recent search on CruiseOnly.com revealed no less than eight seven-day cruises for less than $100/day per person.
Deals such as these are not limited to the Web sites listed here, and they're not difficult to find. Just be certain to read the fine print and quickly book the deals that appeal to you.
If the Caribbean sun isn't for you, how about some cruises designed to show off fall foliage? Click "next" to read more about autumn splendor.