They just need to price it more than the cost of the base stations and maintaining downlink sites. Any revenue above variable costs is worth trying to capture. The cost of keeping the constellation of satellites healthy will be borne by customers in richer regions.

Look at it this way - the satellites will be traveling over Africa no matter what. If no one in Africa subscribes, then that's a part of their orbit where they aren't earning any revenue. Assuming the rest of the costs are covered by subscribers in other regions, they can price service in Africa as low as they'd like (above hardware costs).

I'm guessing the person you're replying to meant the incremental cost of serving African customers is low.

You can get $1 of margin in Africa and $100 in the US/Canada for the same product.

See medicine, for example

Not if your already expecting US/EU customers to pay for the whole thing already