By including a per diem amount in the letter, the parties will not have to execute another payoff letter if the termination date. If you opt to pay for your meals out of pocket, you will be reimbursed your allowable per diem for your trip after your return.Calculate your per diem allowance for your trip. Simply enter your travel dates and details to find out your per diem allowance. GSA establishes the maximum CONUS (Continental United States) Per Diem rates for federal travel customers. Easily find Arizona's per diem rates for your business trip. You can also understand what it would be like if Grand Coulee had been built under the socalled partnership concept of the last several years. I Check the payoff letter and it does not have a per diem amount. In fact it says specificity that will be valid through.