I'm glad that MAW is granting your son's wish. My nephew went on his wish trip last year and it's a memory that the family will treasure forever.
We may be able to steer you in the right direction for additional tickets if you provide a little more information. How many days? What ages? Will you visit one park per day or will you "park hop"? Will you be going to a waterpark or Disney Quest? Once we know some of these details, someone will probably be able to post links to a site with the best possible tickets for your needs.