Hiring a car for a week can be a great option for travel. Avis, the most popular car hire company for this area, offers rental cars for around $841/week on average.
Booking in advance not only ensures a better chance of getting the vehicle of choice, it can save you up to 16% on your car rental. For a below average price, Cheapflights recommends booking your car hire at least 90 days in advance.
Yes, hiring a vehicle in Dakar for a month is certainly possible.