On an annual basis, the department of mental health and addiction services shall determine both of the following using generally accepted governmental accounting principles:
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.
R.C. § 5121.32