Judson:
I have never hunted in Africa, but am somewhat familiar with the income of South Africans. Those amounts seem very high to me. It seemed high if it were for all five people, but if the cook is getting a $2000 tip, it seems like he could quit working for the rest of the year after he gets his tip.
If it were me, I would do some research. Perhaps Safari Club International can help you.
For an American hunt of short duration, I expect to tip the guide 10%, and the cook about 2% or 3% of the cost of the hunt.