To really save money I suggest you check your local library.

They should have several books on WDW that you can check out and then you can decide what you like best. You may decide to buy or just use the library ones. Even if they are a year or two old most of the information is still useful and can be suplemented with the free information you can find here!
I do find that the Unofficial Guide as said above is my favorite. Also the Passporter.