Agents and cruise lines love to promote their cruises, and their ads will boldly display a particular sailing with a "starting at" price - $199/pp, for instance. What you don't see until you investigate a little further is that the $199 cabin is the lead-in price, or the price of the cabin at the lowest category, which tend to be the least desirable in terms of location and size. The cheapest is also an interior cabin. Some people are quite happy with an inside cabin; they like sleeping in pitch-dark rooms and don't spend much time indoors to worry about small spaces. But if you're claustrophobic, need natural light and fresh air in your stateroom, or are squeezing four into a cabin and need room to move around, the lowest-category cabins might not be worth even the rock-bottom fare you see online.
Be sure you know what you're getting. Ask your agent to or cruise rep for details as to the cabin's location, size and nearby noisy public areas which may interfere with sleep. Your agent will be more than happy to find you a great cabin specific to your needs at a price you can afford. The cabin may not be cheaper, but you'll be a lot happier in the end.