Brilliant piece of technology. They still sell for £50 ish second hand on ebay. The price on Logitech/ PC World/ Currys website ranges between £99 and £119.
More info: http://www.logitech.com/en-gb/mice-pointers/mice/devices/3443
Explore your new media universe with a state-of-the-art mouse that's effortless to use - on your desk or in the air. On your desk, advanced laser technology gives you precise tracking and instant response. In the air, innovative Freespace motion sensing transforms hand motions into natural, responsive cursor controls. Sit back and listen to music, browse photos, or surf the Web - from your desk or across the room. The MX Air mouse is the perfect complement to your PC-based entertainment experience.