Can't give you specific dollar amounts, but we found the hypermarche in Tahiti, near the marina, to be very expensive, say 150 - 200% of North American. On the flip side, it was the most incredible supermarket I have ever seen. Take an immense French supermarket and drop it in the middle of a tropical ocean and you get the idea. The market in downtown Papeete was also very good. Baguettes are cheap though.
Heading back to Lake Ontario for this summer. Relatively few stops along the way from Grenada. Martinique, Guadeloupe, St. Martin (must have something to do with the French food), then Bermuda, New England and up the Hudson/Erie Canal. We were going to go via Newfoundland and Labrador but June remembered that one of the kids is getting married this summer - details, details!