It's less than in the US, but I don't think it's quite as low as France. On the upside, you don't have to pay or deal with any VAT.
When I was last at Hermes in St Martin this past March, there were no Birkins at all--they said they really don't get them--but they had a lovely sellier Kelly in Black Togo with PHW for about $4950, I believe. The sterling was much less expensive there than in the states, something like $850 for the GM Chaine d'Ancre bracelet. Scarves were about 20% less than they cost in New York City if you include tax in the NY price.
Hope this helps!