One of the reasons Seattle is such a good team is that they understand that it's better to pay your own players than to pay for someone else's. I mean, look at some of the players Seattle has paid big bucks from outside the organization to come in (minimum 3 years and $5m APY):
Zach Miller, Sidney Rice, Robert Gallery, Percy Harvin, Cary Williams, Jimmy Graham
Hopefully Jimmy Graham earns most of his money, but the rest of the list is made up of guys who were paid far more than their actual value to the team.
Instead, Seattle has made a killing on smaller deals. Bennett was initially signed on a relatively low-cost 1 year deal. Avril was initially signed on a relatively low cost 2 year deal. The team got good value on low end DL signings such as Alan Branch, Tony McDaniel, O' Brien Schofield, Raheem Brock, Kevin Williams, etc.
And at OL, when was the last time Seattle signed a free agent OL to big bucks and it worked out famously? Robbie Tobeck probably comes the closest, and that was 15 years ago. If you count shotgun approach OL signed in large numbers to cheap deals, then Breno would be your diamond in the rough.
And if you look around the league, there are a lot of 'name' OL who leave their team in FA for big bucks, and many of them struggle to be as good with their 2nd team.
I think this is especially true for our team with the requirements Cable puts on his players. With Cable it is less about talent and more about fitting the mold.