Ouch!!!!
It has no chance at that price, I know it's not the same but just look at DJ Hero's price when it was first released, people are just not interested at expensive peripherals it will not have good sales, throughout videogaming history I think there hasn't been a single addon which is expensive that hasn't died a slow death ie: Jaguar cd, 32x, mega cd and many more I can't think of.
But I'm hoping that this is a MS marketing ploy, meaning that they're putting out feelers to gauge the level of pricing that people are willing to pay, but when the actual release is near we might see a drastic lowering of the price wrong footing everybody, similar to Sony's 'bait and switch' with the name 'ARC' which made MS to comment about naming copyrights/legal action only for Sony to pull out the official name 'Playstation Move' .
So essentially I'm hoping MS are not arrogant enough to release a £100-£150 addon.