St Martin is one of the easiest places to check into and out of, but there are only three places to do this.
The first place is at the bridge going over the channel into Simpson Bay Lagoon on the Dutch side. It is in the police station across the channel from the Yacht Club. The second is in Philipsburg, also on the Dutch side. Right now you have to walk all the way down to the cruise ship dock, but I am told the office in the marina will be back up and running again next season. The fees I found on the Dutch side were $21 for me to go into the lagoon (I missed the $7 mark by a foot – it is for 12 meters or less), $20 per week in Simpson Bay or the Lagoon, and $6 to anchor in Philipsburg for three days.
Over on the French side you can only check into Marigot, but you are allowed to anchor anywhere and take a bus or taxi into town to clear in. Customs and Immigration has been moved since I was here two years ago. It is now in a building directly across the street from the dock of Marina Fort St Louis. I was charged $18 to check in and another $18 when I check out.