i think an average of £2 a pack is pretty standard from what i've read on minis before - i think less than £40 is pretty rare.
my cdc charges 1.95 for sachets, and i think 2.10 or 2.15 for tetras and bars.
i LOVE the bars. they make the diet do-able because i genuinely look forward to them, and because they're peerlessly portable.