Better gas mileage and handling, not quite the same wingspan.There’s only one place in the country where you can buy a Boeing off the lot: Paine Field in Everett. But in two years that will change.Soon, air carriers will be able to fly off with a new Dreamliner in Charleston, South Carolina. And when the good people at Uzbeki Airlines and other buyers like them hit the checkout counter, they might notice a big savings on their receipts:The buyers must sign an endless stack of paperwork. In South Carolina they will have to pony up state sales tax, which tops out at $300, even for a jet that can cost $150 million or more.With all the focus on the corporate welfare Boeing will collect thanks to its southerly move, I wonder how we all managed not to notice that buying the world’s biggest plane in Charleston is the sales tax equivalent of buying a lawn tractor in Chehalis.