cousins brings up a good point. Once you book, check the website often. Sometimes the price will drop between the time you booked and the sailing date. If that happens, call who you made the reservation through (travel agent, cruise line, etc.) and tell them you noticed this difference. If the final payment hasn't already been made, maybe they will subtract the difference from the outstanding balance.
If the final payment has been made, then maybe you will get an on board credit for the difference.
2007 - Majesty of the Seas (Bahamas)
2009 - Enchantment of the Seas (Western Caribbean)
2010 - Freedom of the Seas (Western Caribbean)
2013 - Golden Princess (Alaska, roundtrip from Seattle)