Still think cruise could be better. I heard that it is quite cheap for some season. It takes care of the food and board, plus entertainment at night. Lots of American students take the short cruise 3-4 days cruise. It is affordable and convenient.
Did you read that article on MIT BBS travel board about cruising with Norwegian cruise line? Sounds quite interesting to me.
No need to worry about sea-sick. I heard it is barely noticable unless there is a big storm. Also, you can bring a type of medicine called "Dramamine" which is very effective for motion sickness.