Virginblue,
It takes about 20 minutes by car (depending on tractors traffic!).
The ferry takes 2 hours 40 minutes so it's obviously still quicker by air.
Comparing standard fares:
Ferry £95 return
Skybus £140 return
BIH £170 return
Yes a bit cheaper from Lands End but not a big enough difference I would suggest to make many people switch from Helicopter to Plane.
Perhaps the "novelty" factor of flying on a helicopter is the motivator to keep it going?