(a) In lieu of any other contingent expense allowance provided by law for the prosecuting attorney of the Eleventh Judicial District, the prosecuting attorney shall be authorized a contingent expense allowance of twenty thousand dollars ($20,000) per year, to be borne by the respective counties of the Eleventh Judicial District, as follows:
Jefferson County ..................… $17,000
Arkansas County ..................… 2,000
Lincoln County ..................… 1,000
(b) The counties in the Eleventh Judicial District shall pay the above-prescribed annual amounts in equal monthly installments.