You'll find that most of the 7 day itineraries will be the same throughout the cruise lines. Most have the same ports - some interchangeable (ie Belize instead of Jamaica) or (ie Nassau instead of San Juan). There's something for everyone in every port!
Definitely though you are going to want the extra $ for the various expenses. Tips alone is $10 pp/pd + excursions, alcohol, extras. For a 10 day, I'd allow $600-800 depending on your lifestyle.
I don't know of any Southern (other than 10 day) that leave from the US. $1000 pp for a balcony on a 10 day is likely not going to happen. I do my price comparisons at http://www.vacationstogo.com
which is also a good play to compare all lines itineraries and options.
Once you've gone on Princess, they send you all these fabulous email deals ($500-800 for an 8 day in Oceanview for example), but you don't get them until you've gone at least once ... Good luck!