Sorry, no personal experience of shipping to Africa. It just seems, that generally when shipping by sea, the costs at the receiving end often bring a surprise.
Happened to me as well: in 2008 I sent my bike from Australia to Finland by sea, and everything including ocean freight was about 500€ at the sending end. When I picked up the shipment in Helsinki, I got charged 180€ for nothing much at all (picked it up on the first possible day, so no warehousing fees). All in all it was still cheap, but was hard to understand that the first payment included transport half-way across the globe, the 2nd one was just some port handling fees!
And remember, unlike Oz or Finland, seaports can be corrupt in many places, that's when your nerves may really get tested! If the price difference is not huge, I'd go for airfreight, much quicker and seems to generally work better for sending bikes.