If you want cheap flights to Zaire, try to go during November when prices are often at their lowest. At the other spectrum, prices soar in August, as this is a very popular time to visit Zaire.
On average, Kinshasa (FIH) is the cheapest airport for flying into Zaire, so consider starting your trip from there. Searching by month will also show you the cheapest day to fly.
What are you waiting for?