Be it further enacted, That the city manager may sell any city property which is obsolete, surplus, or unusable, without taking bids therefor, if the proceeds of such sale do not exceed five hundred dollars ($500), but sealed bids shall be taken or a public auction shall be held for any sale producing more than five hundred dollars ($500), and any sale producing more than one thousand dollars ($1,000) or any sale of real estate shall be subject to approval by the council.