Further ramblings of a self-made pauper

I have just tried, and failed, to work out how much it would have cost to mount an expedition for six Europeans into the African interior in 1860. Starting from Zanzibar, and travelling by way of Mombasa, with suitable numbers of bearers and askari, total travel time there and back, six months.

I am not sure whether it is google that has let me down, or my lack of imagination in search parameters.

I'm tired now, and I'm going to bed. If anyone has ideas for suitable resources, I'd be pleased to hear...