The conditions for a heavily discounted date from either agency are fairly simple. The savings are, for the most part, created with reserved space. If the sailings you're looking for have increased in price since the agency booked the rates, the savings will be evident. smlev, it may be possible this date has not sold as well todate and therefore has not increased in price w/Disney since either agency held space. You should call the agencies and explain the situation.
With that said, even if you are not saving money, it's been my experience with agencies that the benefits of sailing with a group- even if the price is the same - are worth it. Most of us think in terms of saving- reduced cost- what we don't think about is ADDED value. Gifts in the stateroom, perhaps special events exclusive to your agencies customers, etc. They might not be able to save you $50, but they CAN make your vacation $50 better!
Plus, there are many benefits to going with an agency which specializes in the cruise you're looking for. Getting the dining times you're looking for, help with stateroom assignments, etc. You'll get far more with them in your corner than without.
-starmouse