Have you tried anchoring against that £600 price in the copy/design? Could be compelling.
So it's always been a candidate, but other messages seemed more important, largely because it seems that most people think poor sleep -> sleeping pills, and do not think -> CBT / therapy. As in, it's the immediate frame of reference. That's been confirmed in training/talking to Boots staff, but they have found that reference point useful in making the value case to customers.