This “open-jaw” ticket from SecretFlying.com and ebookers.com can take you from Europe to Africa and back for as little as £269 round-trip.
An open-jaw itinerary is one that leaves from one city, but returns to a different one. In this case, the outbound flight leaves Schiphol airport in Amsterdam, flies to Johannesburg (OR Tambo airport) via Nairobi, and returns to London Heathrow.
Availability: Flights at this fare are available on select dates from April to October 2015. (There are also higher fares and alternate city combinations available.)
How to book: Follow this link to the SecretFlying website.