The board of supervisors of each and every county of the state shall at all times keep within the sum named in its said budget and within the annual revenue, always seeking to lessen expenditure instead of exceeding revenue and budget estimates. The amount appropriated and authorized to be expended for any item contained in such budget must not exceed the amount actually estimated for such item, and the total amount appropriated and authorized to be expended from any fund, except for capital outlay, election expenses and payment of emergency warrants and interest thereon, or for extraordinary court expenses, shall not exceed the total amount actually estimated for all purposes. The total expenditures authorized to be made from any fund shall exclude reserves added thereto, and the total shall not, in any event, exceed the aggregate of the cash balance, excluding reserves, in such funds at the close of the fiscal year immediately preceding, plus the amount of estimated revenues to accrue to such fund, as determined and fixed in the manner herein provided, and the amount which may be raised for such fund by a lawful tax levy during the current fiscal year.