UPS lets you send USPS Priority Mail at their walk-in locations, but a New York Times investigation found Manhattan locations charging up to 140% more for the favor.
It’s perfectly legal, and the amount is up to the discretion of the store, which are independently owned and operated franchises. However, it’s not disclosed beyond a notation on the receipt. Save your cash and ship via USPS at the the post office.
Paying More to Send U.S. Mail at U.P.S. Stores [NYT] (Thanks to Jason!)