We done are own tour in St Lucia had a fantastic day and it was half the price.
We have just done this cruise and have to say you need to book a trip for Saint Lucia as the day you pull in there is a Sunday and everywhere is shut, apart from the little lego shops as you get off the ship. The best port we did was Saint Marrten that was a great day, we caught the water taxi and got off at the second stop and shopped till we dropped. Jewellery and tobacco at prices you wouldnt believe, its a duty free paradise. Look out for electrical goods and cameras at ridiculous price.