There are many ways to save money...if you don't mind staying off-site. The Entertainment book has discounts for some hotels in the area. I got a 1 bedroom suite at the Courtyard for $60 a night using it. You could also book a hotel using priceline to save money. The hotel websites themselves may offer you better pricing.
As posted above, Mousesavers.com has codes to save on a rental car. Using the codes, I was able to get a rental car for about $30 more than it would have been to use Mears transport to get from the airport and back again.
Which gave me the freedom to go to the local grocery store. And since you are allowed to bring food and water into the park, the extra money I spent on that, was saved many times over since I didn't have to buy food and drinks in the parks for every meal or snack.
I see that you have Da Bearsssss in your signature. If you are from the Chicago area, you can look at Milwaukee as an alternative to both Chicago airports.
There is a link on the site for Discount park passes. It isn't much, but even if it is $5 per pass, that's $25 saved. You could also go with a non-hopper pass and stick to one park per day. That's around a $50 per person savings on a 5 day pass.