I used Saint Denise in Reunion as a base for excursion to the mountains, Hell Bourg and Cilaos. Stayed at a camping (booked at Airbnb) which was the cheapest option to stay on that island. If you stay longer Gites (hostels/mountain huts) are also reasonable. Public buses are cheap and efficent. Food is reasonable in bakeries but can be quite expensive in restaurants. Some Supermarkets have the most amazing things from France (for a price!).
The last day I was there was a unexpected holiday, most restaurants and almost everything else was closed.
Euro is the currency as the island is part of France and you find a lot of AT&T, but changing money is next to impossible and definitely not at the airport, be prepared.