Each member of the board of directors of any authority which operates a public water system, a public sewer system, or a fire protection facility in Mobile County and which serves 6,500 or more customers, in addition to any other compensation, shall receive an expense allowance for performance of his or her duties in an amount of fifty dollars ($50) for each duly called and attended special meeting of the board of directors. Notwithstanding the foregoing, the expense allowance for special meetings attended shall not exceed one thousand eight hundred dollars ($1,800) per year per member.