The county commissioners of any county shall have the power to appropriate any sum out of the county treasury not otherwise appropriated, for the purpose of erecting or building in such area other than the county seat of such county, a jail or holdover, for the use of such county and area cities in which such jail shall be erected. Nothing in this act shall be construed as preventing the area cities from joining and cooperating with such county in the erection thereof, nor to exclude the authorities of any area city in such county which any jail that shall be so built from the use of such jail for the use of the cities.