Book the best cabin, you can afford, now. If there are any cabin "guarantees" take that. You may get an upgrade. If you wait there may not be a cabin available and you will be out of luck and be stuck with the air.
Royal Caribbean does not allow discounting of their cruises, so an agent cannot sell the cruise for less than Royal Caribbean is selling it. An agent may be able to add on board credit, free insurance or other incentives into the bargain but the price of a Royal Caribbean cruise will be the same. The only exception is group space and that wouldn't apply on a cruise this close to departure.
Take care and enjoy the cruise.