To get from Nosy Be to Saint Marie means going via Antananarivo, whether you fly or use ground transport, unless you want to be truly adventurous.
It is possible to go by taxi brousse via Ambilobe and Vohemar down to Antalaha where you could get a passage on a cargo boat to Sainte Marie. If you only have two weeks though, that is not really a realistic option, as you may have to wait several days in Antalaha for a boat to leave. Also accidents with these cargo boats are too frequent for comfort and many of them result in fatalities.
Overland, you would take the ferry from Hell-Ville to Ankify, pick up a taxi or local taxi brousse to Ambanja and from there take the taxi brousse to Tana. That will take the best part of 24 hours. From Tana, you take a taxi brousse from the Eastern taxi brousse station to Tamatave – a company called Vatsy is probably one of the safest and most comfortable. That will take all morning and into the afternoon. From Tamatave you get a taxi brousse to Soanierana-Ivongo, with any luck straight after your arrival from Tana, and from Soanierana you get the ferry the following morning to Sainte Marie. So: if there are no hold-ups, two and a half days. Taxis brousse are inexpensive – you can probably do the whole trip to Soanierana for around 35 euro or less per person, but the ferry is relatively pricey, as the operators have taken to surcharging foreigners.
Of course, you can also hire a private car and driver, which will cost you probably between 40 and 60 euros per day depending on your bargaining skills and what’s included, plus the fuel for the driver’s return trip.
Regardless of whether Air Austral is a good airline or not, it isn’t clear to me why you’d want to get to Nosy Be via La Réunion. If you took Air Madagascar into Tana, you wouldn’t have to wait much longer for a connection to Nosy Be, and you’d have the advantage of the substantial discount that Air Mad offer their long-distance passengers on their domestic flights. This might also make flying for all or part of the trip from Nosy Be to Sainte Marie more affordable.
At present their website isn’t yet taking online bookings for August, but it may well be worth the wait. It’s also an inconvenience that they still haven’t fixed the part of their website that used to allow you to book discounted domestic flights online together with the long-haul flight. The solution to that is to call either the Paris Call Centre or Aviareps, who are their authorized consolidators in London (contact details on the website) to book your flight from Tana to Nosy Be. Any other domestic flights can be booked more cheaply once you’re there.
Air Mad, by the way is nowadays pretty good again, and the Airbus they fly into and out of Paris is in any case operated, crewed and maintained by Air France, even though it is painted up in Air Mad colours.
