USPS have standard shipping rates which are the same for the given type of packages, but the shipping rates may vary depending on where the package is sent from and sent to, package type, time, etc.
Although the shipping rates may vary depending on the package, and the destination to where it is sent to, however, USPS also offers Priority Mail Service which delivers the package in 1-3 days and has same flat shipping rate no matter where you are sending your package.
You can find more about USPS Shipping Rates from the USPS Postage Price Calculator which will tell you about the exact shipping rates depending on the information provided.