I just list with a flat rate that is the same for everybody, based on past shipping experience. Depending on the buyers location, I might over or under charge, but it all evens out in the long run. They know and agree to the shipping rate before they purchase, so there are no surprises, and it takes the guess work out of providing exact shipping rates. I’m in Wisconsin, so shipping to either coast is nearly the same, with the west coast usually being a little higher. I have noticed that USPS rates are a joke now for large packages. I used to use them for everything, but now FedEx is typically $10-$15 cheaper on average for large packages compared to USPS, and they get it there much faster. USPS now only gets my small stuff. Everything else goes FedEx.