Accommodation on Sainte Marie (and Île aux Nattes) is varied and caters to all budgets. Whale-watching season (July to September) and Christmas/New Year are peak seasons, when you should definitely book ahead. If you're planning to stay four nights or more on the island (which we highly recommend!), consider splitting your time in two separate areas: north and south of Sainte Marie or Sainte Marie and Île aux Nattes.
Like everywhere else in Madagascar, the vignette touristique, charged per night, is added to your hotel bill. On Sainte Marie, there is also a taxe de séjour, a one-off fee for the duration of your stay.