In counties containing a population of two million or over and employing a registered engineer as road commissioner, the board of supervisors may authorize the moving, relocation, or reestablishment of detention camps by force account or day labor where such camps are used in connection with county highway construction or maintenance work, if the board determines that such work of moving, relocation, or reestablishment can be done more economically and satisfactorily by force account or day labor than by contract, and that the total estimated cost of new or additional building structural materials necessary to be purchased in order to perform such work does not exceed five thousand dollars ($5,000).