When you can find one on sale, the R9 270X is around $200. If you want something slower and cheaper, the R9 270 is a little bit cheaper and slightly faster in most games than a GTX 660, which would be the next option.
You don't want either card. The card you want is a r9 270 (non x). This card is the same as 270x except just a lower clock speed, you can easily overclock it to 270x speeds and save 20 bucks. 270x is nearly twice as fast a a 260x but the price difference is only 60 bucks (40 bucks difference for the 270). Bad part is they have been selling like hotcakes and are nearly out of stock, there is only one model left in stock on newegg: