The authority provided by subsection (a) may be used only if the Secretary of Defense determines that Federal payments and commodities provided under section 20 of the Richard B. Russell National School Lunch Act (
42 U.S.C. 1769b) and section 20 of the Child Nutrition Act of 1966 (
42 U.S.C. 1789) to support an overseas meal program are insufficient to provide meals under that program at a price for students equal to the average price paid by students for equivalent meals under a comparable public school meal program in the United States.