(b) If the infrastructure revenue bonds are then redeemable, the price of the purchase shall not exceed the redemption price then applicable, plus accrued interest to the next interest payment date thereon. If the infrastructure revenue bonds are not then redeemable, the price of the purchase shall not exceed the redemption price applicable on the first date after the purchase upon which the bonds become subject to redemption, plus accrued interest to such date. Upon purchase or redemption, the bonds shall be canceled.