£250 is what I paid. And this controls resistance automatically so you can close your eyes and hit your power numbers without having to fuck around with gears or even looking at your garmin/computer. Quite nice.
I rarely change gears on my dumb trainer. Pick one that gets power and cadence right, ride, done. £300 to avoid changing gears for some intervals isn't selling me the concept and I own a Computrainer :P
At £400 though, why not buy a Powertap wheel and a cheap turbo?
You can then train with power everywhere and have a turbo setup with power.