Any property owner prepaying an assessment for a special improvement district, within 30 days from the publication date of the final assessing ordinance, shall be charged interest on the bonds issued to finance the district only from the time interest begins to accrue on the bonds through the 30th day of the prepayment period. The city shall bear the cost of paying any difference between the interest on the bonds paid by the property owner and the interest due on the bonds at the next payment date. (Code 1979, § 34-156)