What grounds would you be suing Disney on? How would they have violated your rights by not giving you a discount?
I would ask that you please learn a little more about the ADA before suing. You may find there is much to learn. Disney does an outstanding job for those of us with disabilities, and we would really prefer not to annoy Disney in any way. If Disney or any other company thinks that disabled people are trying to take advantage of their kindnesses, then they are less likely to offer those kindnesses in the future.
I love Disney because it is one of the few places I feel "normal." (whatever that is) I can do everything like the rest of my family, and I am not stuck sitting at the doors of shops because there is a step, or waiting in the front of the store because the aisles are too narrow (usually, anyway).... I love Disney for all they do, and I appreciate it. Please do not dismiss the kindness they give us, above and beyond what is legally necessary.
I am sure someone here can give you a link to the ADA and sites which explain what is required.