That sounds about right for the retainer. Any types of appeals are a very expensive and time consuming process, so do not be surprised if the final bill exceeds $25,000. Depends quite a bit on what you are appealing, and whether it is state or federal courts. I've seen legal bills for an appeal run over $250,000, and that was in a state court, not federal.
You, personally, must write a letter to the court telling what you did, it is called an error of omission and saying what you really want.. You need to have some good reasons for why you want to live with your Dad so you better talk to him or a counselor about that. Why you were not told what to expect in court and helped to say what you wanted and not be intimidated by the circumstances is just stupid. You give the letter to your Dad to take to his lawyer who must reopen the physical custody hearing and ask for a new date to rehear the matter. You also must talk to your mother about your feelings and about going back to live with your Dad, you might want to do this with a counselor or CPS agent or social worker present who can help keep everyone calm and let you get what you have to say said. This process is going to take a few months at least but it will work if everything comes out up front and honest. Going to CPS behind your mothers back is the dumbest thing you could do unless you are actually being physically harmed when in her care.