Actually, any agent can get you the same price plus they represent you and not the cruise line. Booking directly with the cruise line is not advisable because if you have any problems, who do you think they represent?
It's always best to book with an agent because they represent you and have alot more information than the cruise line's representatives. Many of them have never even been on a cruise and are only interested in making a sale.
Plus, they only represent one cruise line. Should you want to consider all your options, including other cruise lines, they are no help whatsoever.
Bottom line is to find a reputable agent you feel comfortable with and let them help you with all the arrangements.