The board of county commissioners of any county wherein such ambulance service has been established pursuant to section 31-3901, Idaho Code, prior to July 1, 2020, is authorized, in its discretion and under such terms and conditions as it deems appropriate, to enter into a cooperative agreement with adjacent counties or fire protection districts and for private individuals and corporations to provide ambulance service for such county or counties or a portion thereof. All cost of said service shall be apportioned equitably among the participating counties and fire protection districts, as determined by their respective boards of commissioners.