It really depends on the income of both parents. It can range anywhere from a few hundred dollars to a few thousand depending on this. I have been on disability for serveral years due to a back injury while on active duty military. But, because my wife makes too much money on her job, I was not eligible for SSI. I hope this helps you, but, I would contact an attorney. Most of them have free first consultations. If you decide to use one, they would take a percentage of back pay. Usually 25%. It takes 12 to 18 months if you are turned down, but, I don't see why you would be if the child is autistic and requires special needs.