Of course, it would depend on the cruise line, but I would strongly suggest that you find a cruise professional near you to handle the reservation. Without sounding like a broken record, I will point to this article that you might find enlightening:
Most cruise lines are doing everything they can to guarantee consumers a level price playing field so that they can book where they feel most comfortable. The days of getting bargains from on-line discounters are long over.
The whole price issue is basically smoke and mirrors, because it depends on when you book your cruise. May of 2006 should yield you some pretty good prices because it is shoulder/off season in terms of demand. Find a cruise professional that will continue to monitor the pricing and then go to bat for you when prices drop or adjust.
Just my opinion.