Out of the amount of money appropriated by the governing body of such cities to meet the expense of the police department for the ensuing fiscal year, the police board shall, on or before May first of each year, adopt a budget for the police department for the ensuing fiscal year. Said budget shall itemize purposes of expenditure by organization units, activities, functions, and character classes in not less detail than “personal services”, “contractual services”, “commodities”, and “capital outlays”. Such budget, when adopted and certified by the board, shall be the authorization of expenditures for the purposes set forth therein. No transfer from one character classification of expenditure in the board budget to another character classification shall be made without the approval of said board. A copy of said budget and notice of subsequent transfers shall be deposited with the chief of police and the secretary of the police board and copies thereof shall be prepared and available to the public upon request.