I think that even if they amnesty Arenas and let Redick and Anderson walk, they'll still have around $50 million in committed salaries, and another $3 million worth of cap holds. That's $53 million, on a cap projected to be somewhere around $58 to $60 million.
They might be able to save another approximately $3 million by using the "stretch" exception, but that only knocks them back down to $50 million. They'd still be, at minimum, $5 million to $8 million short of being able to sign CP3 or Deron.
Trading Jameer Nelson for nothing, or including him in a S&T for one of the star point guards, is plausible, but I don't necessarily consider it likely.