Taxi's are very expensive around Saint-Louis. The price goes up when they have to go over a bridge, so ask them to stop before they enter the bridge to drive into town and pass the bridge on foot. Also: it's not true that the prices go up in the evening, at least not for locals, for tourists they will always try to make an unreasonable high price. Doubling of the price when it gets dark is absolutely not true, don't let them fool you! Though you might have to pay a little extra, otherwise you won't find a taxi back home.