The district may provide for the payment of all necessary preliminary expenses actually incurred in the making of surveys, estimates of costs and revenues, employment of engineers and other employees, making of notices, taking of options, legal and clerical help and all other expenses necessary to be made and paid prior to the authorization for the issuance of such revenue bonds, provided, that no such expenditures shall be made or paid unless an appropriation has been made therefor in the same manner as is required by law for district funds. Any funds so expended by the district shall be fully reimbursed and repaid to the district out of the sale of such revenue bonds before any other disbursements are made therefrom, and the amount so advanced by the district to pay such preliminary expenses shall be a first charge against the proceeds resulting from the sale of such revenue bonds until the same has been repaid as herein provided.