I need help getting a car seat?

my 2 year old granddaughter has scoliosis & has to wear a body cast. she is unable to sit in a car seat, but they have a special one for kids with this problem. but her insurance won't cover it. does anyone know of an organization that will help, [it cost $449.00] we have to get this because she has to lay down in the backseat whenever she goes anywhere, and that is just not safe, very dangerous. please let me know. we live in michigan