 Luxury brands have had a pretty good year, if you look at the number of them opening up their own e-commerce sites. On Friday, it was announced that the parent company of Saks Fifth Avenue has signed a deal to buy upscale rival Neiman Marcus Group, which owns Neiman Marcus and Bergdorf Goodman stores. The price tag? A little over $2.6 billion, with online behemoth Amazon holding a minority stake.