If you don't mind changing planes, you may want to consider flying to Luanda (LAD), Luanda Angola via Lisbon on Air Portugal.
Go ahead and book your flight to Luanda NOW!
In order to get the lowest available airfare, book your flight to Luanda as early as possible, since the cheapest seats are booked months before departure. If you are flexible depart on the first Tuesday of the month, as there are usually some great deals and discount airline tickets on offer.