This is a difficult question, while eco-tourism brings in money, what is the cost to the environment of flying to the Congo in order to explore the forests for example and see the wildlife.
Perhaps one way to help bring in income to local people and the wider economy is to find a way to help people sell locally made items around the world, but items that are hand made and not mass produced, so each item is a reflection of local culture but also has the attention to detail of that hand made item.
Photography is one way to do this, if the locals, armed with a camera go out and take photos of the local communities, wildlife, buildings, architecture then these can perhaps be printed and sold, but sold as a numebered lot, 1/1000 - 1000/1000 for example, so they are limited editions.
Creates employment but also avoids the mass produced items associated with tourism.
Science research is also a big thing, so if people are to fly to the Congo, then priority can be given to those seeking to study what is there, could be anything from undergrarduate, to research, work with the local universities and allow the same reciprocal arrangements, so UK / Congo universities work together for example.
Accomodation could be very simple, but have solar power + inverters to power devices for example.