All payments made by the secretary under this chapter, shall be, insofar as possible, supplementary to payments to be made to a day training center or group training home, or a combination of both, by the persons with developmental disabilities resident in the home or center. Payments made by the secretary under this chapter shall not exceed actual costs for the care, treatment, support, maintenance, and training of any person with a developmental disability whether at a day training center or group training home or combination of both.