Installment payments; interest; costs included in assessment

The assessment may be levied to be paid in one installment or in not more than five installments at the discretion of the governing body, and when installments are certified to the county clerk, interest at the rate specified on the scrip or bonds hereinafter authorized to be issued shall be added: Provided, That when scrip or bonds are not issued the interest on the one installment shall be four percent. The assessment shall include the cost of materials, labor, engineering and supervision, publication expense, cost of printing bonds, removing old sidewalk, and all other expenses properly chargeable against the project: Provided, That certain costs not ascertained at the time of figuring the expense, such as publication of the assessment ordinance, printing of bonds, etc., may be estimated: Provided, That the costs relating to scrip or bonds shall be deducted if the assessment is paid within the thirty days provided for herein.