The special court may, in its discretion, direct any appropriate state agency, in addition to the Commission on Local Government, to gather and present evidence, including statistical data and exhibits, for the guidance of the court. The court shall determine the actual expense of preparing such evidence, other than that secured by the Commission on Local Government, and shall tax such expense as costs in this case; the costs shall be paid by the clerk into the general fund of the state treasury, and credited to the appropriation of the agency furnishing the evidence.