such costs, including the cost of modifying such loans, shall be as defined in section 502 of the Congressional Budget Act of 1974: Provided further, That such amounts obligated in a fiscal year shall remain available for disbursement for the following 8 fiscal years: Provided further, That funds made available in this Act and transferred to carry out the Foreign Assistance Act of 1961 pursuant to section 1434(j) of the BUILD Act of 2018 may remain available for obligation for 1 additional fiscal year: Provided further, That the total loan principal or guaranteed principal amount shall not exceed $8,000,000,000. Trade and development agency For necessary expenses to carry out the provisions of section 661 of the Foreign Assistance Act of 1961, $100,000,000, to remain available until September 30, 2025, of which no more than $24,500,000 may be used for administrative expenses: Provided, That of the funds appropriated under this heading, not more than $5,000 may be available for representation and entertainment expenses. VII GENERAL PROVISIONS ALLOWANCES AND DIFFERENTIALS 7001. Funds appropriated under title I of this Act shall be available, except as otherwise provided, for allowances and differentials as authorized by sub chapter 59 of title 5, United States Code