There are certainly descrepancies in pricing , I do not believe as far apart as you indicate. Like airline fares, cruise ship rooms are subject to things like early booking discounts, last minute discounts. There are plans where you can book a guaranteed catagory of room and not be assigned to a room until the last minute. There are last minute deals to fill last minute unfilled rooms. There are agents reselling group fares they have booked and on and on and on.
Do some homework. Narrow things down to ship, cruiseline, itinerary , time of year ,type of accomadation etc. etc. . Decide when you can travel. Do you need to book now for next year or , can you wait for a last minute bargain? Are your schedule and cruise desires flexible or must you have a specific cabin on a specific ship, for a specific cruise. Get prices from several sources, pick something you can live with, book it, and don't look back.