Arriving in St. Martin is a little more complicated than most Caribbean Islands because you have to choose - will it be the French side or should it be the Dutch side? When we arrived at 3 AM we chose to anchor in Simpson Bay so by default we got the Dutch side. Had we continued sailing another three miles or so we would have anchored in Marigot Bay - the French side. The next decision to be made is "should we go into the lagoon?" In the lagoon boats are not rolled around by the ocean swell but it is still very windy, which makes dinghy trips kind of wet. To enter the lagoon boats pass through a draw bridge (both on the French and the Dutch sides) and both bridges are open three times during the day. Separating the French and Dutch sides of the lagoon is the 760 meter Causeway bridge, constructed in 2013. This bridge is a swing bridge and opens to coincide with vessel traffic that has entered either of the drawbridges.
Curare falls into the 8-13m classification and these are the costs, if your yacht is larger you will pay more. The Dutch bridge charges US$7.00 per entry (no exit fee), the French bridge charges nothing. Once a boat is in the lagoon there is an anchoring fee, a different fee depending on which country you are in. On the Dutch side you pay a harbour and custom fee of US$7.00 and then a weekly anchoring charge of US$20.00 (this also applies to Simpson Bay), even if you only stay for one day. On the French side the harbour and customs fees are zero and it is free to anchor on the French side of the lagoon. Judging from the number of boats that go through the Dutch drawbridge and then immediately motor over to the French side this is the cheap cruiser option. Apparently if you go through the French drawbridge it is not easy to get to the lagoon anchorage area because boats must follow a narrow dredged channel and without local knowledge it is easy to go aground, so cruisers use the Dutch bridge but do not check in on the Dutch side - thus avoiding the costs..
If you decide you want to visit the French side but you do not want to go into the lagoon you will anchor in Marigot Bay and there is a one time fee of 20 Euro and then 0.25 Euro per meter per day (1 to 3 days) or 0.35 Euro per meter per day (over 3 days). However I heard a discussion on the local net this morning and the conclusion was that most cruisers do not pay to anchor in Marigot Bay. To travel from the Dutch to the French side, or vica versa, you must pass through the Causeway swing bridge and the charge is listed as US$7.00 (stated in the tourist literature, but is this fee ever collected? How do the officials know if you went through the swing bridge, there is no one taking notes.)
In conclusion - anchoring on the French side of the lagoon is the least expensive option but if you choose to anchor outside of the lagoon then Simpson Bay is your best choice (depending on the wind and swells). Keep in mind that if the information from the local VHF net is true then anchoring in Marigot Bay is free, but it is a long dinghy trip to the Dutch side where most of the cruisers hang out.
Just for interest I have included a photo from February 26, 2015 showing Steve Job's mega yacht, "Venus", leaving the lagoon. This boat is 256 feet in length and 39 feet wide, which means Curare could sit on it's deck crosswise. I wonder how much Venus paid to be in the lagoon?