The board of directors is authorized to investigate the financial condition of each person liable under Section 6 and is further authorized to make determinations of the ability of each such person to pay the sums representing maintenance charges, and for such purposes to set a standard as a basis of judgment of ability to pay, which standard shall be recomputed periodically to reflect changes in the cost of living and other pertinent factors, and to make provisions for unusual and exceptional circumstances in the application of such standard. The board may issue to any person liable therefor statements of amounts due as maintenance charges, requiring payment in such manner as may be arranged, in an amount not exceeding the average per capita operating cost as determined under Section 7.