[Request] How expensive must Unobtanium be per kilogram to justify mining it on Pandora and shipping it back to Earth?

Of course certain unrealistic things to consider, but I still wanna find out if the estimate from the movie is in any kind of range of possibilities.

1. Distance from Pandora to Earth is 4.37 lkght years, ship takes 6 years

2. Costs of building and maintaining the station

3. Mining and refining

4. Shipping and transfer to Earth

I would also be happy, with a comparison on how much a farming of moon stone per kg would cost.