The West African CFA Franc has a fixed exchange rate to the euro. 655.957 or in street trade often 650 F CFA is equal to €1, and roughly 500 F CFA is equal to 1 US dollar. There are banks in all the major cities, and most of the banks have cash machines. As in all the CFA Franc economies, Visa is much more popular than Master Card. For Master Card and Maestro withdrawals, try Banque International du Bénin blue star, with SGBB red and black square logo being quite reliable with Visa and Visa Electron. Keep in mind that many businesses and offices, including banks, close for several hours in the middle of the day.
Prices for goods purchased in a store, restaurant, hotel, bus tickets, etc. are non-negotiable, but almost everything else is. Depending on the item, it's not uncommon for foreigners to be quoted a price that is double the final purchase price.
If you have been on the road a long time and are looking for a nice, cool and well stocked shop, try Erevan hypermarket very close to Cotonou Airport. It is reputed to be the biggest hypermarket in all of West Africa, selling all the nicest imported French goodies, as well as having a nice hardware department.
For the tourist wanting to experience the local spread, Dantokpa Market in Cotonou is the biggest local market in West Africa.
One can find any type of African commodity all over Benin.