We had trouble finding discounts as well, other than the multi day pass.
You definitly get rewarded for staying loyal to a park system (i.e. Disney or Universal) as the per day cost reduces dramtically. For example, as I am sure you know, the pass from 4-5 days is only $10 or $20 more. It is really great in that way.
We purchased Disney Gift Cards from Target at a 5% discount and then called Disney to redeem and purchase passes, as you can't use more than 2-3 gift cards on the website.
This saved our family $200+ - was an extra step or two, but well worth it as we had 13 tickets to buy.
Finally - I wouldn't wait until you get there to buy the passes if you can afford to do so. They FastPass System is so amazing and you will be way behind if you wait until you are there to register.
Disney Property Guests can sign up their Fast Pass 60 days prior and Pass Holders can sign up starting 30 days in advance.
It is hard to plan ahead, but for the long line rides; it is well worth the process. It is a 1st Class Experience with the Fastpass, but you only get three and the more you plan the more efficient you can be with your day.
We had an amazing time --- it has been 20 years for me since I last went and it brought back so many great memories. We learned so much after we got there that I wish I had known (like FastPass). But Disney is worth every penny -- I have never talked to a person who walked away disappointed.