Every school district board of directors may authorize children attending a private school approved in accordance with RCW 28A.195.010 to ride a school bus or other student transportation vehicle to and from school so long as the following conditions are met:
(1) The board of directors shall not be required to alter those bus routes or stops established for transporting public school students;
(2) Private school students shall be allowed to ride on a seat-available basis only; and
(3) The board of directors shall charge an amount sufficient to reimburse the district for the actual per seat cost of providing such transportation.