The cost and expense of purchasing and acquiring property and of purchasing or constructing the irrigation works and improvements mentioned in this chapter shall be paid out of funds raised for such purpose. In case bonds, or the proceeds from the sale of any series of bonds, are insufficient for the purpose for which they were issued, additional bonds may be issued after submission of the question, at a general or special election, to the electors of the district. Additional improvement warrants may be issued to supplement warrants already authorized and issued. Such bonds and improvement warrants must be paid in the order of their priority.