I know I should hate the idea of trading Walker, but then I remember Michael Pineda. Even really nice prospects still have to prove they can stay healthy with MLB workloads. Seattle tried to trade Walker + Franklin for a very good outfielder last offseason and just missed out. In terms of WAR, Price is basically just as good as said outfielder, though he'd have less team control.
Deep down in my heart I know that the Cano move is more bad than good, and I know the a Price trade is probably a bad idea long term. But if Seattle adds both Cano and Price, you are talking about by far the best 1-3 rotation in baseball, maybe one of the best 1-3's in baseball history, and you are also talking about a 10-12 WAR boost to a team that has had a 75 win baseline the last few years. That alone won't get them to the playoffs, but if they make a few nice moves around two with the remaining resources and then have a few pleasant surprises next season from the younger core, you are looking at a well rounded, 85-95 win team. And if they make the playoffs with a rotation like that, I really like their chances.
I'm not going overboard here, the Mariners probably won't be world champs any time soon and making the playoffs is still going to be hard, but at least the Mariners have some hope now, and at least there will be actual intrigue over a Mariner's season for the first time in about four years.
I just wish Cano played the outfield. Seattle has a bunch of 4th and 5th outfielder types, which is how guys like Ibanez and even Mike Morse got so much time in the corners last season.