How could one use a | tablet | for those with special needs?

My son has Voluntary Mutism, and Cerebral palsy. He doesn't walk, His only word is home and he uses it for all purposes. He actually has a vocabulary of thousands of words. If you hold 2 cards up and a toy bus, he will point to the one that says bus. The school had a very expensive Assisted Audio Communication (AAC) device $ 7000 US. Last year we bought a Ipad for my wife, mainly to read, She got a APP that has icons he uses to communicate. A full blown touch screen computer works best for him with the GUS program, its flexible and we add our own Icons. He is 12 years old but can operate AAC devices very well, try it they are not easy to learn. Qualities we look for Durability, flexibility, can be used in school, mounted to wheelchair or stand in front of chair. Can play videos to keep him occupied in restaurants.