I was with you until you listed the $ requirement. You say $650 doesn't include taxes, but are you including tips in there? That will add a bit of money to the cost. I think you can find some shorter cruises that might make it close to your $ requirement, but it'll be a little tough. Have you checked out
www.icruise.com ? You can try searching for a cruise that will meet your requirements, and just might luck out. Good luck!