You've gotten some good advice but here's my "rule of thumb" that I've used for years to estimate the cost for dining out when I travel. It works not only for St. Martin but for places all over the world. You can use it to calculate the cost of one meal or for your entire trip.

It's really simple - You estimate what you'd spend if you ate a similar meal and drank a similar number of cocktails and/or wine at a similar type restaurant (i.e. casual, moderate or upscale) back home. Do this for each meal you think you have while traveling. Add 15% to 20% to that total number and you'll come up with a very workable "meal budget" for your trip and you'll probably have a little money left in your pocket at the end of your trip.