Hi Don,
We're going the opposite way to you, currently in Khartoum going south on three motorbikes.

We've had nothing but positive experiences in Egypt and Sudan with officials and fixers.

More info here:
http://www.horizonsunlimited.com/tstories/thomas

In particular the following postings:

Sudan and arrival in Khartoum
Knock knock
On Looking After Us Foreigners
Into Africa
New Numbers Please

You need to use the tourist police to get a vehicle into Egypt. But it's free (tip appreciated). But you pay for everything else, customs, road tax, insurance etc etc.

Also you need the fixer at Wadi Halfa. Not free but not extortionate either. There are two of them and in our opinion they do a good job, very friendly and efficient.
Two 4X4 travellers on a tight budget tried to do it without him. If you ask him (we did) he says it is possible to do it yourself without his service. But we gave up.
The two 4X4 travellers had a real good attempt at it, but eventually had to give up. But the fixer gave them a reduced rate for their troubles.
We came to the conclusion you can do it yourself - IF you speak fluent Arabic.
The Wadi Halfa fixer even arranged to get me a CD of the particularly good music being played in a cafeteria close to the main hotel in town.

We have met a number of people going the other way, northbound. None has mentioned the need for a fixer south of Sudan.
The general advice seems to be that borders get easier the further south you are.

Cheers

__________________
TTR250 - London to Cape Town