(a) Each participating municipality shall pay to the retirement system an expense contribution prescribed in accordance with this section.
(b) The board of trustees, before January 1 of each year, shall set the rate of the contribution necessary to provide an amount required to pay the difference between:
(1) the estimated administrative expenses for the following year; and
(2) the anticipated revenue, from sources other than municipality contributions, to be used for the expenses of the year as adjusted for a surplus or deficiency existing on January 1 of that year.

(c) The rate set by the board of trustees under Subsection (b) may not exceed 50 cents a month for each member.
(d) The board of trustees shall certify the rate set under Subsection (b) to each participating municipality before January 1 of the year for which the rate is set.