By including a per diem amount in the letter, the parties will not have to execute another payoff letter if the termination date. The Payoff Amount and Per Diem Amount quoted herein are effective through December 31, 2020.GSA establishes the maximum CONUS (Continental United States) Per Diem rates for federal travel customers. The Per Diem Method. Upon written request of Beneficiary, Grantor agrees to reimburse Beneficiary for the full cost of narrative appraisals of the Real.