There might also be an issue with time differences.

I know some of the cruise lines have 24 hour sales. So if you saw a price that was really cheap and it was gone within a few hours, the 24 hour sale may have ended. This could explain the difference in cabin prices. The lowest, cheapest cabin category sold out and the better cabins were now 'cheaper" than the lower categories.

Cruise fares are like airfares. If it's what you want and it's the right price you'd better buy it then. I think VacationsToGo even says this on their limited time offers. They say to call right away to book the fare.