Any comprehensive plan submitted pursuant to this act may include the purchase of selected correctional services from the state by contract, including the temporary detention and confinement of adults convicted of crime. The secretary of corrections shall annually determine the costs of the purchase of services under this section and deduct them from the grant payable to the county or, in the case of cooperating counties, the grants payable to the counties. In no case shall the charges for correctional services under such contract with the state exceed in cost the amount of the grant the county is eligible or, in the case of cooperating counties, the total amount of the grants the counties are eligible to receive under this act.