Most important question is how much time do you have?
One thing I can tell you, and I know people do not listen is do not rush it. People post stuff like 30days to Dar and back or 15000km round trip in 20 days through SADEC countries, it's stupid and beyond comprehension why anybody would want to rush such trips. You mis on all the nice stuff in between. You must really get to feel the places you ride and stop over at a place for 2 or so days. Rather do one country properly than chasing through 3 of them and only see the main road.
I started a thread here about what to pack for an extended trip.
http://www.wilddog.za.net/forum/index.php?topic=69799.0All the info on a Carne is here
http://pikipiki.co.za/planning-and-preperation/carne-insurance You only need a carne for Egypt, no other African country.
http://pikipiki.co.za/planning-and-preperation/visa-informationExcept for Ethiopia which you have to get a visa in South Africa, you can not get one in Kenya. Sudan you can get in Ethiopia, most other Sub-Sahara countries you do not need visa's or a Carne for your bike. Tanzania is a months off on allowing SA citizens in without visa's.
West coast up is difficult, Angola for one is difficult to get into, you get the Visa from PTA and have to take your letter of invitation. For the rest of those countries the visa's are quite expensive.
http://pikipiki.co.za/planning-and-preparation.
For the rest take a few dollars for border taxes and when you get into trouble.
You can do it cheap, eat local food, buy beer and water only in bottles with sealed tops. You do not need to take water filters and such as there are water to buy every where. If you want take some tablets with.
Camping cost on average R50-R100.
Why people pay places like Cytech to ride is beyond me, it's expensive and as far as I know they ride form dawn to dusk through Africa. It's the same as doing JHB to CP and back 15 times, you see zero. Do it yourself it is fun and you can do it on your time. In a tour you are bind by their schedule, it's kak end of story.