If there be within the city limits 640 acres or more of land, the governing body may divide the area of the city into 640 acre drilling units and consolidate any excess area with lands owned by others in the same manner as hereinafter provided for cities having less than 640 acres within the city limits. If there be no suitable drilling site for any unit available at reasonable cost within the corporate limits of the city, the governing body is hereby granted power and authority to acquire by lease or purchase a suitable drilling site outside such limits.