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.
Finished the circumnavigation in early February in Grenada. Have to work on a book project for the next several months so the boat will be waiting for next year.