Another arm who just graduated from the Mariners farm system, Bryce Miller is in a very similar mold as Woo as a starter but has found better production to this point for Seattle.
Miller is 7-3 in his first 14 MLB starts with a 3.96 ERA in 75 innings. While he is striking out less than a better per inning right now, he has the stuff to be a "strikeout guy" and his 1.00 WHIP is extremely encouraging.
While Miller will not command nearly the haul that Gilbert would, I do think he would cost a bit more than Woo, and it may come down to a straight up swap for one of Nootbaar, Gorman, or Donovan, should the Mariners choose to make a move.
That's the difficulty here. Seattle does not have to trade with St. Louis, and they could easily wait until the offseason to make a move for a bat. But if they do choose to go ahead and get that bat with control that the industry says they are searching for, then St. Louis makes the most sense.