The limitations set forth in Section 20921 may be exceeded to a maximum of fifty thousand dollars ($50,000) for projects and purchases of materials for projects for which no assistance from federal, state, or other local governmental agencies is requested, if that approval is secured from the landowners of the district representing at least two-thirds of the assessment valuation of the district, or if no assessment has been collected within the prior year, by the landowners representing at least two-thirds of the acreage within the district. The approval may be obtained either through a special election held for that purpose or by written consent of the approving landowners. The special election may be conducted by mail ballot.