As soon as any such contract is let, the city council is thereupon authorized to issue and dispose of bonds of the city in amounts sufficient to pay for the total work to be done under such contract. Unless bonds are disposed of for such purpose, the contract shall not be performed and shall not be binding upon the city. Bonds issued under the provisions hereof shall be denominated grading bonds, and shall state upon the face thereof the street or part of street to be graded from the proceeds thereof. Such bonds shall be due and payable in five years from date thereof, shall draw interest at a rate not to exceed the rate of interest specified in section 45-104.01, as such rate may from time to time be adjusted by the Legislature, payable semiannually, shall have interest coupons annexed, and shall not be sold or disposed of below par, and the proceeds therefrom shall be used only for the purpose of paying the costs of the grading for which issued. Such bonds may be sold or disposed of in the manner deemed best or advisable. As the work of grading progresses, partial estimates may be allowed and paid and the final estimates paid as soon as allowed.