The legislative body shall, in the ordinance providing for the issuance of revenue bonds, fix the initial schedule of minimum rates, rentals, fees and other charges for the use of, and for the service and facilities furnished or to be furnished by, each parking facility. After any parking facility has been in operation the legislative body may revise such schedule of rates, rentals, fees and charges from time to time, subject to the provisions of any lease theretofore made by the parking authority or parking division and then in force. The parking authority or parking division shall charge and collect the rates, rentals, fees and charges so fixed or revised. Such rates, rentals, fees and charges shall be so fixed and revised as to provide funds sufficient at all times (a) to pay the cost of maintaining, repairing and operating the parking facility or parking facilities, including reserves for such purpose and for replacements and depreciation, (b) to pay the principal of and the interest on the revenue bonds as the same become due and reserves therefor and (c) to provide a margin of safety for making such payments.