Clearvista-travel-bids is a great free service which can help you find the best airfare. For more information on how it works, read about Brigada-Travel Bids (same service, different name) at Missionresources.com.
Notice: The following agencies advertise discount travel fares for missionaries. People have asked me if this is a business. It is not. We don't profit from these links. We have not used these services, and we make no warranties, express or implied. Be sure to investigate any agency carefully (as you would any Internet company) before you do business with it.
Adventure Travel Service advertises discount travel fares for missionaries.
AFC Travel specializes in international travel for missionaries, exchange students and adoptive parents. In business since 1994, their site says, "It is our 'heart' to see that short-term and long-term missionaries are able to travel the world spreading the Gospel of Jesus Christ."
A&R Associates does 95% of its business with Christian missionaries.
Missiontravel.org exists to help organizations save money on mission travel through discounted international airfare.
World Missions Tours International has been serving missionaries for 30 years.