A free agent starter is what he SHOULD do, because that way we get to keep Stroman and Sanchez. Then, if they are looking good and cheap, he can trade off a more expensive Bueurle or Happ.
Problem is, Tanaka or Garza may simply want more than he'll pay, OR want to play for another team for the same amount of money as AA will offer.
Certainly, a cost controlled younger starter via trade would be fantastic, but might cost either BOTH of those guys, or one of them and a major league position player. He probably can't make the team better by doing that.