Pricing also depends on the specific week that you are cruising. Cruise lines know when the high demand, shoulder and the soft departure weeks. Their pricing reflects the overall demand for the particular cruise. As an example, if you want to cruise over Christmas and New Years, be prepared to pay full bore and book as soon as you can.
But, if you are going to cruise, say the first part of December, history has taught us that you are much better off to wait until the last minute to book.