Just play around. Cheaptickets usually has some good prices on cruises. Expedia, Travelocity, Orbitz. They’re probably all priced about the same, but it never hurts to play with numbers and see what you can get.
I’ll tell you with the balcony, though… you really don’t need one in the Caribbean. It’s just all blue, everywhere. If you want to see something, you can go to the top deck and look out. The rooms at the front of the ship and the back of the ship are best. They’re sideways, so you’ll get two to four big, round windows, depending on location. It’s really fun to watch the ship dock (front rooms) and be able to see where you’re going. You don’t spend all too much time in your room, so the balcony on a Caribbean cruise is pretty much a waste, if you ask me.