The bonds shall be sufficient in amount to pay for the proposed improvements together with necessary incidental expenses connected with the improvements, but the amount shall not be more than the amount specified in the order and notice of election. The total amount of the bonds shall include:
(1) the amount of the engineer's estimate;
(2) incidental expenses;
(3) organization expenses; and
(4) cost of additional work caused by any change or modification made by the directors.