Southern Idaho Bureau of Reclamation Repayment Act of 2007 - Authorizes any owner of land within the A&B Irrigation District in Idaho to repay at any time the construction costs of District project facilities that are allocated to such land. Provides that, upon full payment of such costs, the parcels shall not be subject to specified ownership and full-cost pricing limitations under federal reclamation law, for which the Secretary shall, upon request, provide the landowner a certificate.