The designated costs of issuing the refunding bonds may be paid by the purchaser of the refunding bonds or may be paid from any other legally available source, including the general fund of the city, other available revenues of the city under the control of the legislative body, the proceeds of sale of the refunding bonds, the interest or other gain derived from the investment of any of the proceeds of sale of the refunding bonds, any other moneys in escrow or in trust or any combination thereof as the legislative body may determine.