Purely Gadgets are selling it for £177.95. Like people have said the extra buttons, increased frame rate (using the EN-EL4A battery) and its made of magnesium alloy mean its more expensive than the other grips.
How solid is the grip on the camera? That was the one thing that got me to swap out my D200 for a D2x as the grip on the D200 felt "wobbly" and I was worried it would snap off the camera. I didn't bother spending £250 on the grip when I ordered my D300 yesterday as it's a second body to my D3 and I wasn't sure how solid the grip would be.
Pete
Mine certainly feels rock solid. I've not used a D2X or D3 to compare it, but as far as imconcenerned im happy carrying the camera around by the grip with a long lens on.