The warrant shall be drawn for an amount equal to the sum of:

1. (a) The excess of the par value of the refunding bonds directed to be sold over the amount for which the board has determined the refunding bonds may be sold, which shall not in any event, exceed 10 percent of the par value of the refunding bonds directed to be sold.

2. (b) An amount sufficient to pay interest at the rate provided in the refunding bonds from the date of sale thereof to the date of the maturity of the bonds to be refunded out of the proceeds of the sale.

   Items (a) and (b) are incidental expenses of the district as defined in Section 51336.