Try contacting a few different providers and get competing quotes for same dates/stateroom categories. Some to consider include
DCL,
Dreams Unlimited (the sponsor of these boards), All Seas, All Seasons, Vacations to Go,
AAA, Costco, Icruise and others(Travelocity, Expedia).
Many who post here will testify their experiences, but you will hear more positives than negatives about any particular provider. The bottom line is you should look/compare for yourself.
Happy hunting!