Seattle finished in fourth place in the AL West last season, largely due to an offense that ranked 22nd in runs scored and 28th in batting average. Butler would immediately step in and become a middle-of-the-order presence, having hit .289 with 15 home runs and 82 RBIs in 2013.
To acquire Butler, the Mariners would likely have to part with one of their major pitching prospects. Seattle has one of the strongest pitching systems in baseball, featuring Taijuan Walker, Danny Hultzen and James Paxton. Considering the Royals are probably going to lose Ervin Santana in free agency -- he's asking for $112 million over five years -- acquiring a top arm would appear to be a must for them, especially as they attempt to win before the contract of James Shields runs out.
The Mariners were about average offensively in 2013, but could lose both Kendrys Morales and Mike Morse from their lineup, as well as Raul Ibanez, who will be 42 years old and can't be expected to repeat his 29-homer season even if he does re-sign.
The one downside for the Mariners -- besides cost -- is that Butler is strictly a designated hitter at this point in his career. That clogs up that spot in the lineup, which would keep manager Lloyd McClendon want to rotate players through it. If he hits, though, the Mariners will deal with that.