We're not going to sign him anyway, so what's the point of speculation about the price :) I'm talking in principle.
I see some similarities between Martial-Rashford and Sterling-Sane pairs. Martial and Sane look more naturally talented than their counterparts, at least technically. But both don't seem to be fond of the hard work off the ball, both lack defensive discipline, lose the ball carelessly, hence don't fulfill their potential as team players.
Sterling and Rashford, on the other hand, are more humble and ready to work their socks off in every game, at least that's my impression. It's the type of wing forward Pep loves, I think discipline and defensive contribution mean no less to him than pure attacking talent.