Periodically, US Airways runs a sale on buying their frequent flyer miles.Usually, buying miles is no bargain.But when they offer you double the miles for the same price Over at View from the Wing, the bottom line is clear: With this offer you can buy 40,000 miles for $1030, get 80,000 miles in return, and fly business class from the US to Europe. Or if you and a friend each have 40,000 miles, you transfer to each other for $430 apiece, and you now both have 80,000 miles — enough for a business