Cheap Kilimanjaro flights are not easy to come by.
Kilimanjaro has its own international airport, Kilimanjaro Airport, but it's tiny and not many airlines fly to it.
The major airlines offering flights to Kilimanjaro airport are the African Air Tanzania, Air Kenya, Ethiopian Airways and the European KLM.
But Kilimanjaro airport is not the only international airport in Tanzania...
If you want to relax on the beaches in Zanzibar after your climb, like most travellers do, or if you want to combine your Kilimanjaro climb with a safari in Tanzania or Kenya, then consider flying to or from Dar es Salaam or Zanzibar in Tanzania, or even in Kenya. Those flights will work out cheaper.
Budget travellers and backpackers with more time and money should definitely check out all those options carefully. A bus trip is not the most comfortable way to get around Tanzania, but it's an adventure in itself and a cheap one as well.
If time is at a premium, or if you are flying to Tanzania solely to climb Kilimanjaro, then a flight to Kilimanjaro airport is the best option.
Kilimanjaro airport is located half way between Arusha and Moshi, about 50 km from each. It doesn't get much more convenient than that!
Kilimanjaro flights from Europe are the most convenient of all. KLM fly the route Amsterdam - Kilimanjaro -Dar es Salaam daily.
Any Kilimanjaro flights from other continents involve a change of airlines once in Africa.
Ehtiopian Airways offer Kilimanjaro flights at good prices from Addis Ababa via Nairobi. (They also fly to Europe and a handful of other international destinations.)
Kenya Airways offer flights to Kilimanjaro from Nairobi three times a day. The flights are operated by Precision Air, a young and dynamic Tanzanian airline with competitive prices. I can recommend them. Precision Air also operate flights from Dar es Salaam or Zanzibar to Kilimanjaro.
The other local carrier is Air Tanzania who operate Kilimanjaro flights from Johannesburg in South Africa and also connecting flights from Kilimanjaro to Dar es Salaam and Zanzibar.
If you are booking your Kilimanjaro climb through an overseas agency they can usually also arrange your flights for you. But do check the prices and options yourself as well.
In my experience it works out cheaper if I do it myself, and not only because agencies charge commissions. An online broker specialising in cheap flights can usually come up with a better offer.
Good luck with your search for a cheap Kilimanjaro flight!