$315 is a lot of money for a frame with such a big dent.

I wouldn't worry too much about the few spots of rust, but it is a bit bothersome that it seems to be rusting from below the paint.

There are a few methods for dent removal.

1) Tube replacement
2) Rolling the Dent with blocks (and repainting)
3) Someone suggested freezing with water somewhere.

Maybe if the frame was free... with $50 shipping... but that seems unlikely coming from Japan.