The department shall periodically determine the individual cost, exclusive of the cost of education, for the care, support, maintenance, and treatment of the patients in each state institution and for persons receiving treatment prescribed by an institution following release or without being admitted as a resident patient. In making such determinations, the department may use averaging methods for each institution if, in the judgment of the department, it is not practicable to compute the cost for each patient. The cost of capital expenditures and capital construction shall not be included in making such determinations.