The term of said franchise shall commence with the effective date hereof, and continue and remain in full force and effect for 50 years, or until such time as the grantee shall surrender or abandon same or said franchise shall be forfeited for noncompliance by the possessor thereof with its terms, or the state of California, said county, or other public or private corporation thereunto duly authorized, shall purchase by voluntary agreement or shall condemn and take under the power of eminent domain in accordance with then existing law all property actually used and useful in the exercise of said franchise situated within the unincorporated area of said county. Said franchise shall never be considered or taken into account in fixing the value of said property in excess of the actual cost to the grantee hereof in procuring the same.