The proceeds from the sale of any bonds issued under division of this article may be applied only for the purpose for which the bonds were issued, except any premium and accrued interest received in any sale must be applied to the payment of the principal of or the interest on the bonds sold, and if for any reason any portion of the proceeds are not needed for the purpose for which the bonds were issued, that portion of the proceeds must be applied to the payment of the principal of or the interest on the bonds. The cost of acquiring any project includes the following:

(a) the actual cost of the construction of any part of a project, including architects’, engineers’, and attorneys’ fees;

(b) the purchase price of any part of a project that may be acquired by purchase;

(c) all expenses in connection with the authorization, sale, and issuance of the bonds to finance the acquisition;

(d) the interest on the bonds for a reasonable time prior to construction and for not exceeding one year after completion of the construction.