I am so sorry for all the craziness that you are having to go through. My husband is active duty and we have Tricare Prime(South). I have been told by everyone including Tricare that I will not have to pay anything out-of-pocket. Someone mentioned a $12 fee for the Psych Eval. $12 is pennies for a surgery that is going to change my life forever.
It sounds to me like your surgeon's office needs to be audited by Medicare. He can not bill you for the amount that Tricare does not pay. He has to accept their payment. If he is audited, then he will have to repay every single dime that he has collected from overcharging his patients.
Hang in there! Hopefully, you will get things figured.