Well nVidia has slashed their prices like within the last two weeks to compete. The 4870x2 was the same price as the 280 when it came out. AMD just hasn't responded with price drops yet. Right now at this particular moment, nVidia has the upper hand again in price-performance, however bear in mind that AMD does not necessarily have to lower it's price on the 4870x2 because two 4830s in crossfire beat the 280 for about 240 USD.