You never mentioned if you're traveling by car or by bike. It's true that is different, but still the actual procedure is the same. The difference comes from the way you are perceived by the customs official. With a car you have more money so you pay more... even if the reality is different (you can travel with a 5000USD 25y old LandCruiser or a 15000USD brand new 1200GSA).
I have have traveled from june 2011 to august 2012 from Morocco to Egypt without a Cpd and in the end I payed 625USD for TIP's, Laisser Passez or other custom papers.

Here's what we've payed exactly and what borders we've crossed:

Morocco - Tanger Med - free, just registered at customs
Mauritania - 10E when entered and asked and payed 10E at exit but just because was the first weeks in Africa. In reality you don't need to pay twice
Mali - Gogui - 10000CFA Laissez Passer (normaly 5000CFA but we arrived on Sunday) + 5000CFA police registration of the LP
Burkina Faso - Koro - 5000CFA LP
Togo - Senkanse - 5000CFA LP
Benin - ?? Near Aneho - 5000CFA LP
Nigeria - Seme - 7000 Naira at Seme Border (1000 bribe to stamp passports, 4000 TIP, 2000 Bribes in order not to pay a bond); apparently at Nikki the TIP is free; payed 1000 Naira to extend the TIP for a second month at Mfum
Cameroon - Ekok - 7500CFA 15 days Laissez Passer (no one checked that it had long expired when we exited)
Gabon - Bitam - 10000CFA LP after hours fee (normally 5000CFA until 6 PM)
Congo - ?? Doussala - 10000CFA LP(asked 20000 but negotiated to 10000 - probably possible for 5000)
DR Congo - entered through a small border near Luozi and managed to pay nothing; exited through Kasumbalesa and managed not to go to Customs (very big border post); is not recommended to do so as you can have to haggle to exit (it happened to us in Benin)
Zambia - Kasumbalesa - TIP Free, Road Tax 50000 Kwacha (can avoid paying it)
Namibia - Katima Mullilo - No TIP, just road Tax 140 Nam$
SAR - Vioolsdrif - nothing just waived through
Lesotho - Sani Pass - There's 30 Rand bike tax but we've payed 100 Rand for visas, tax and everything
Bothswana - Grobler's Bridge - 240 Pula (Auch) Permit, Road Tax and Insurance (no papers just a receipt) other reports suggest that this practice is random
Zambia - Kazungula - TIP Free, Road Tax 50000 Kwacha (can avoid paying it, second time we didn't pay)
Mozambique - Cassacatiza - 27 Meticals TIP yeah that's almost 1US$
Tanzania - Unity Bridge - 25 USD TIP
Kenya - Taveta - 20 USD TIP
Ethiopia - Moyale - Free (just completed a form (TIP) and asked for a copy of the registration paper)
Sudan - Metema - 15 Sudanese Pounds for TIP (~3USD).
Egypt - Aswan - Now the funny part: 2500EgP (410USD) for a CpD from the Auto Club of Emirates with 2 pages. Egypt is insanely expensive if you travel with your vehicle; besides Cpd we've payed some extra 700Egp (115USD) to enter from Sudan (Custom clearance, plates, licence, fixer commission) and 2150EgP(350USD) to exit towards Turkey (1250 Custom Clearance, 750 Shipping Agent Commission, 150 Storage in Port Said)

Cheers from Bucharest,
Ionut

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Crazy Oyibo - From Romania Into the World.
Part I - Africa Full Circle http://blog.intotheworld.eu