The board of county commissioners of each county shall provide the county or district engineer with suitable offices, conveniently situated, and such assistants, equipment, supplies and clerical help as are necessary for the proper performance of his duties: Provided, That in counties having a population of more than five thousand (5,000) and less than seven thousand (7,000), with an assessed valuation of more than fourteen million dollars ($14,000,000) and less than seventeen million dollars ($17,000,000), in which there is located a city of the second class and at least two cities of the third class, the salaries, expenses, and clerk hire provided for herein may be paid out of the general fund, or out of the consolidated road and bridge fund, as other county bills are paid.