How much does flat rate priority cost?

As of my last update, the cost for Flat Rate Priority Mail from the United States Postal Service (USPS) varies depending on the size of the box. For example, the cost for a Small Flat Rate Box is around $9.45, while a Medium Flat Rate Box is approximately $16.10, and a Large Flat Rate Box is about $21.50. Prices may vary based on additional services, so it's best to check the USPS website for the most current rates.