Normally, the rates you pay thru PayPal are the same as you would thru USPS. PayPal uses a 3rd party service for it's links to the USPS system. Not all shipping features are available thru the selections offered thru PayPal.
You need to do some comparisons on the USPS web site as it appears that the Priority Mail Regional Rates are higher than the standard Priority Mail rates however, depending on the weight, Regional Rates can be much better. For example, I compared a box with a size of 12 x 10 x 2 going Priority Mail and the same size box going Priority Regional, both to the same location. Also the weight was the same for both. My cost for the standard Priority Mail was $6.02 while the Priority Regional was $8.90. Note too that if you calculated the same but, used the maximum weight for Regional Rates, the cost for using the Regional service would be much cheaper than the stadard Priority Rate.
You really have to play around with the different options to see what's works best for you. Box size and maximum weight are important in your calculations. Then toss in the Flat Rate options and now there's another choice.
Point is, this has nothing to do with PayPal as everything is based on USPS rates and services.
