This may not be helpful if you are trying to find a hotel as cheaply as possible, but I strongly encourage you to stay on site at universal for the express pass benefit. That will be a very busy time of the year, especially with Diagon Alley opening, and the express pass can save you an hour wait per ride! One night gets you two days with the pass, so you could do your 5-6 nights at disney, then drive over to universal very early, check in to take advantage of the early entry and then enjoy the park with no lines! The next day you check out and still have the whole park day with the express pass. You can then either start your drive home and find a cheaper hotel to break up the ride (if you're driving, sorry I can't remember the details of your trip), or you could even check into universals "value" hotel, which doesn't offer express pass, so you're still close enough to take a break in the day. We loved our on-site experience at universal so much that our next trip to Orlando will be just universal. Not waiting in lines just completely changes everything!
As for extra dining credits, you can "splurge" with a character meal or dinner show that requires two credits. Have fun planning!