Ganymede is a prize, and I've said before that I claim it for myself, and I'll keep saying until I can plant my flag on it and then keep saying it. There's more water there than on earth...
The benefits of gravity can be had without landing on a planet. Theoretically, you could walk on a satellite that's in geosynchronous orbit. I don't think anyone's tried it yet... But assuming that's true, and I think it makes sense you could have the refining job in orbit and still pay a fraction of the cost that it would cost to get out of an atmosphere. That also makes sense because transport of ores is better done as a stream of pellets into a receiving orbit than as a spaceship with cargo.
