The State Board of Education is hereby authorized to procure space for the storage of such pupil-transportation units while not in the possession of a school district and to pay the necessary cost thereof from the “Special Transportation Revolving Fund.” When any such unit is returned to the State Board of Education, said Board is hereby authorized to recondition same, and to pay necessary cost of such reconditioning, including the cost of any new tires or tubes required for such purpose, from said “Special Transportation Revolving Fund.”