Help with special needs bike for Christmas!

This is my son josh he has cerebral palsy and epilepsy due to a stoke at birth.  We was told he would most likely never walk but this child has proven the doctors wrong. But now he is facing a new challenge that I want to help him concur ( but I can't financially). He wants to learn to ride a bike.  With right side weakness and seizures it will have to be a special needs bike but they are way out of my price range.  I know a bike doesn't  seem like a need but this is something that would really boost his self-esteem.   Help me make his Christmas wish come true.