The lots so surveyed shall be appraised under the direction of the Secretary of the Interior and sold under his direction at not less than their appraised value at public auction to the highest bidders, from time to time, for cash, and the lots offered for sale and not disposed of may afterwards be sold at not less than the appraised value under such regulations as the Secretary of the Interior may prescribe. Reclamation funds may be used to defray the necessary expenses of appraisement and sale, and the proceeds of such sales shall be covered into the reclamation fund.