priority letter cost for USPS depends on the weight, size, and destination of the item. USPS offers Priority Mail for letters and packages that need faster delivery, typically within 1 to 3 business days. For smaller items like letters, the cost for USPS Priority Mail starts at around $8.00 for a flat-rate envelope. Prices can increase depending on the weight and size of the item, with larger packages or heavier letters costing more. USPS also offers a variety of flat-rate boxes and envelopes, allowing customers to ship items at a fixed price regardless of weight, as long as they fit within the designated dimensions. Priority Mail is an excellent option for those needing fast, reliable delivery at an affordable rate.