Return Expenses Paid and Yielded Act or REPAY Act This bill modifies certification and reporting requirements related to certain defense equipment sales to foreign countries or international organizations, and limits the President's authority to waive various research, development, and production costs charged to the buyer in such sales. The President shall, in the certification submitted to Congress for a sale of major defense equipment of $14 million or more, provide information about any waived or reduced charges for the proportionate amount of nonrecurring research, development, and production costs in the sale. The certification shall include additional information such as the type of waiver provided to the buyer, the justification for the waiver, and in certain instances the manner in which the sale would help standardization between the buyer's forces and the U.S. Armed Forces. The President may not waive such nonrecurring charges if the buyer has received (1) $16 million worth of such waivers in the past two years, (2) 15 waivers in the past five years, or (3) $425 million worth of waivers in the past five years. The bill also allows Armed Forces salaries and civilian benefits costs to be included as chargeable administrative expenses related to such defense equipment sales.