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Currently, it is $759 at newegg. For about $300 you can get a GTX 1060 6gb which isn't nearly as fast, but is a great card for the price and is a little more versatile in some of the coins it can mine profitably like ETH.

is it better to buy 1 powerful card or buy 2-3 cheap cards? what is more profitable in terms of mining .

Unfortunately that requires a little bit of fortune telling, because you need to look into the future to see where prices are going. At this moment in time it is slightly more economical to by one really good card like this one instead of two less expensive cards. But that could change tomorrow depending on market conditions.