If you go to the auto mechanic and pay 900 upfront because he tells you that's the cost. Do you expect him to send you another bill stating you owe him another 2300? NO, of course not. If he can't charge the correct fee upfront or at the end of the procedure, that's not your fault as the consumer, that's his as a business owner. If the medical field can't get there house in order to send out a bill or estimate a cost, then that's a big problem.