In order to reimburse the public employees' retirement system for any increased costs occasioned by the provisions of this chapter which affect the retirement system, the director of retirement systems shall, within thirty days of the date upon which any affected employee elects to take advantage of the retirement provisions of this chapter, determine the increased present and future cost to the retirement system of such employee's election. Upon the determination of the amount necessary to offset the increased cost, the director of retirement systems shall bill the department of enterprise services for the amount of the increased cost: PROVIDED, That such billing shall not exceed eight hundred sixty-one thousand dollars. Such billing shall be paid by the department as, and the same shall be, a proper charge against any moneys available or appropriated to the department for this purpose.