The school board of any school district that provides transportation for pupils to and from the public schools may, by agreement with the officials of a non-public school, provide transportation, at times when the buses or other conveyances are not needed for public school student transportation, for students attending the non-public school to and from activities sponsored by that school. Such a school board providing transportation under this Section shall make a charge for furnishing that transportation in an amount not less than the cost thereof, including a reasonable allowance for the depreciation of each vehicle used in that transportation.