It's among the newer cards they've made, so the price tag will be high for some time. They've started announcing the 700 series cards now, so 600 will start to come down.
I bought a GTX 560 ti 448 card earlier this year for £150 and it provides enough power for me. I can overclock it a lot for extra power, and it's SLI compatible.
But having said all this, even though it maxes out almost every game so far, I don't mind turning graphics down - some people do.
Still, I wouldn't pay more than £300 for a graphics card, it's only one component out of many that will determine how good your PC will play games.
(Unless you have an unlimited quantity of money, In that case, get two GTX Titan's in an Asus Sabertooth motherboard with an i7 processor and 16 GB of RAM)