No officer or employee shall during any budget year expend or contract to expend any money or incur any liability or enter into any contract which by its terms involves the expenditure of money for any purpose, in excess of the amounts appropriated for or transferred to that general classification of expenditures pursuant to this charter. Any contract, verbal or written, made in violation of this charter shall be null and void. Nothing in this section contained, however, shall prevent the making of contracts or the spending of money for capital improvements to be financed in whole or in part by the issuance of bonds or notes, nor the making of contracts of lease or for services for a period exceeding the budget year in which such contract is made, when such contract is permitted by law, nor the expending of money out of the contingent fund or other reserves or other surpluses for town purposes after the approval of the same by a majority of the total elected membership of the council.