Seattle is paying most of their defensive players, even their LBs. They are paying their QB, and their RB, and their top TE. Hauschka is making decent money for a kicker.
At some point there have to be places you don't pay, and after Rice and Harvin didn't work out as hoped, I think the team is probably putting WR on the frugal list. OL is definitely on that list too.
OL and WR are two areas on the team that the Hawks merely need to get by with. I can't blame them for the strategy, as WR and OL tend to be very expensive to acquire and keep.
For that reason, I would be pretty surprised if Seattle dropped serious money for an OL from another team. I think they'd only do it as a last resort.