I would go ahead and put in a request to DU and see what price they quote. In the meantime you can check other prices. You don't have to give DU a deposit until you accept the quote (usually a few days) and if you don't like it you can just ignore it and nothing is lost!
I haven't paid much attention to the DU offers since I have two existing reservations with them and not looking for another at this time. Aren't they offering both on board credit plus their usual rebate? If so, make sure you take into account the onboard credit will be available for charges while sailing, and the rebate reduces the cost of the cruise itself before sailing. Not sure if they are offering both.
Regarding DU, we have been vey satisfied with their pricing and service. I'm sure you can get better prices at times other places, but for a new cruiser, its nice to know they are experts on Disney cruises if you need specific help. Some of the cutrates are lost when it comes to specific help.