Anyway, its all covered in this book Mining the Sky
The resources described show how even such a high cost, high risk venture could return nearly unlimited profit. Earth's entire "domestic" GDP would be insignificant.
And don't give up on the Moon. The Japanese Kayuga has discovered Uranium on the surface... turns out lunar morphology ain't what was suspected.
There's a solid metal asteroid out there, by the way... no one is quite sure what kind of metal, but it's a half-mile of something heavy, and it ain't carbon.