In counties having a population of not less than thirteen thousand, one hundred and twenty-five (13,125) and not more than thirteen thousand, one hundred and forty-five (13,145), according to the last preceding Federal Census, the County Boards of Trustees may make such provisions as they deem necessary for office and traveling expenses of the County Superintendent of Public Instruction; provided that the amount of such expenditures for office and traveling expenses shall not exceed the sum of Six Hundred Dollars ($600) per annum. The amount allowed shall be paid in the manner and in accordance with now existing laws governing the maintenance of the office of the County Superintendent.