(1) The cost of the buy-up represents the difference between the fare actually paid and at least the cost of the least expensive first class fare actually available for sale at the time of the buy-up (including, if applicable an instant Y-up fare); or

(2) The cost of the buy-up is any amount, including an amount less than #1 (heck, even vastly less than #1, if UA so sees fit), but all elites holding confirmed space on the flight and on the upgrade list (whether by CPU, miles, or other upgrade instrument) have already been upgraded.