In short
Martinique is a French department: the euro, French social security, mainland mobile coverage and no formalities. That is what sets it apart from every other island in the Caribbean arc.
The north is volcanic and covered in rainforest, dominated by Mount Pelée. The south is flat and dry, and holds the beaches — Les Salines, Anse Dufour, Grande Anse.
What it really costs
The cost of living is the permanent local subject: food costs thirty to forty per cent more than on the mainland, importation and the octroi de mer levy included.
Housing follows the same logic, and a car is essential: public transport is limited and hire is the second item in the budget.
What nobody tells you
Hurricane season runs from June to November. The carême, December to April, is the dry season and the high season for prices.
The flight from mainland France is long — eight hours — and its price swings sharply with the calendar. French school holidays double the fares, more than the local season does.
Sargassum mainly affects the Atlantic coast, to the east and south-east. The Caribbean beaches on the west are largely spared.