Subject to the limitations in subsection (a), purchases and commitments to purchase and sales under subsection (a) may be made without regard to the limitations of existing law (other than section
1341 of title
31, United States Code), for such quantities, and on such terms and conditions, including advance payments, and for such periods, but not extending beyond a date that is not more than 10 years from the date on which such purchase, purchase commitment, or sale was initially made, as the President deems necessary, except that purchases or commitments to purchase involving higher than established ceiling prices (or if no such established ceiling prices exist, currently prevailing market prices) or anticipated loss on resale shall not be made, unless it is determined that supply of the materials could not be effectively increased at lower prices or on terms more favorable to the Government, or that such purchases are necessary to assure the availability to the United States of overseas supplies.