The rates DO change. If a cruise has lots of space 45-60 days before sailing, it is likely to be reduced significantly. They seem to change on Mondays and at the beginning of the month. Some January cruises were recently reduced, but it seems they sold at the reduced prices as they are now increased again. We have booked short notice cruises at bargain prices a several times.
The prices increase as the ship fills. They figure that if you want a particular date, you either booked early or will pay for that date at the last minute. SO....we booked DD's "birthday cruise" early as we wanted that week. The price has now increased significantly. Converesly, had we just wanted any Jan/Feb cruise, we could have saved a significant amount of money by taking one of the recent "sales." Flexibility and sailing "off season" can save you real money.