The board shall establish the beginning and ending of its fiscal year, which period shall constitute its budget year, and, at least thirty days prior to the beginning of the first full fiscal year after the creation of the authority and annually thereafter, the treasurer shall prepare and submit to the board a tentative budget. The tentative budget shall be considered by the board, and, subject to any revisions or amendments that may be determined by the board, shall be adopted as the budget for the ensuing fiscal year. No expenditures in excess of the budget shall be made during such fiscal year unless expressly authorized and directed by the board.