I sailed the Navigator of the Seas last October and also sailed the Mariner in the summer of 2004. I would compare the two very favorably. I wrote a review with a ton of pictures of the Navigator OTS located at
I suspect that the pricing is so high as February is in huge demand. The cruise lines have been successful at gradually raising their rates since the recovery after 9/11 and if you haven't priced one recently, there is an element of sticker shock.
I wouldn't hesitate to book the Navigator of the Seas again.