Most, if not all,Ex-Pats living in the Caribbean purchase Medical Evacuation Insurance in the event they have a serious medical condition and want to flown back to the US for treatment. There are a number of very reputable companies that offer policies including SkyMed, MedJetAssist, Global Rescue, Medexassist to name a few. It's important to read and understand the policy terms fully BEFORE purchase - some companies evacuate you to hospital of your choice, others to nearest major hospital. Some require you be hospitalized locally and under the care of a local physician who recommends evacuation while others will decide on a case by case basis. Annual premium cost of coverage depends on type of policy and how many days per year you remain out of your home country but it is relatively inexpensive (usually around $500/year).

Sorry, can't comment on day to day medical insurance costs in SXM as I live on a different island but I can tell you that on my island you only want to be treated for simple ailments like a cold or the flu and basic "first aid" as quickly as possible.. If you have anything serious you want to go back to the the US (or your home country).

For what it is worth, Medical Evacuation can be very costly, think in terms of $20,000 to $30,000US per flight so Med Evacuation Insurance is a "must".