Cross that bridge when you come to it, securing young players on bargain deals like Bennett for 5m and Avril for 15m over 2 years shows that players are happy to take a little less in order to join a team they really believe is a contender - and it helps that Carroll has built up a "player-friendly" image - cutting Washington is a perfect example, Washington claimed that Tampa Bay offered a draft pick but the Seahawks cut Washington to allow him to choose his own destination.
It's likely that the pick offered was immaterial (probably a 7th or even conditional based on performance), but treating players like that doesn't go unnoticed.
Still, there's no point avoiding signing players because you anticipate not being able to pay others in 2-3 years time. All it takes is (god-forbid) a career ending injury to Russell Wilson to make you look foolish for not taking a punt on Percy Harvin, for example.