On an annual basis, the department of mental health and addiction services shall determine both of the following using generally accepted governmental accounting principles:

(A) The applicable per diem charge for each hospital operated by the department;

(B) The ancillary per diem rate for each hospital operated by the department.

In determining a hospital’s applicable per diem charge and ancillary per diem rate, the department shall consider the average actual per diem cost of maintaining and treating a patient at the hospital or, at the department’s discretion, the average actual per diem cost of maintaining and treating a patient in a unit of the hospital.