That's illogical on two fronts:
A) Saying Bradley cost the Sox "nothing" is a fallacy, since they signed, developed and now pay the league minimum to Bradley.
B ) The system is a direct comparison between Ellsbury and the player currently occupying his position for the Red Sox. No use further complicating the comparison just because you want to point the FO's failures in their deployment of resources. We're all well aware of that, but it's out of the scope of what slasher is trying to track/compare.