The board shall annually include in its budget the amount of money deemed necessary for maintaining any of the public parks, public welfare projects or hospitals operated and maintained as contemplated by this act; provided, however, that the amount so raised by such appropriation shall not be less than one-half of one mill on the dollar, nor more than three-quarters of a mill on the dollar of the assessed valuation of the taxables and ratables of the county.
N.J.S. § 40:32-2.4