There are of course, Yovo (white person) surcharges, but prices can be and should be negotiated.
The general rule of thumb is that when you haggle, start with a quarter or a third of the original asking price, you will usually meet at 50%. Be consistent!
I have found that this does not necessarily apply to food purchases at the fruits and vegetable stands. Ask around how much you would expect to pay for a mango, an avacado or a pineapple.
A liter of gasoline will cost you around 600 CFA, a liter of water around 300 CFA. A baguette is around 175 CFA and half a pound of local coffee will cost 1,200 CFA. A beer in the supermarket will cost your around 350 CFA, at an expat restaurant this will be around 1,000 CFA. A coca-cola will cost you between 200 and 400 CFA in the supermarket. "Western food", mostly imported from France, can be found in supermarkets, but is more pricey than in Europe.