In trades? Kluber and Archer might be available if the Indians and Pirates want to dump salary (and in Pitts case they will have a new front office that are more likely to tank than try to win now). I would think you wouldn't need to give up a top prospect to acquire either of those guys if they were available. Although, Archer signed one of those "I'll bend over and let Tampa F me for my entire prime" contracts so he's still cheap enough for the Pirates to hold on to even if they rebuild.
In free agency, the middle group of free agent Sp's are probably all realistic. Gibson, Pineda, Roark, Miley, Porcello, etc, etc.