I noticed your "about me" mentioned that your son is a special needs child. You may want to consult the family worker at his school about getting your son tested. He/she may know of a center or doctor that may be willing to test for minimal or no charge.
These days, doctors are like double agents. They work for you but they work for insurance companies, too. There's probably an age requirement policy. He may not fall into a particular category.
Is your son in public school? I'm not sure what your school system is like, but if you have a doctor for the student body, you may want to consult him/her as well. Normally they conduct physicals and medical evaluations free of charge.
Good luck! And God bless you in your efforts in helping your son. You're a GREAT mom!