In the Florio article one of the comments mentioned the pick being a 6th rounder. Probably just some fan pulling that number out of his ass, but still, it wouldn't surprise me. Seattle wants 4th round value, and the deal was reported to be two picks, one in 2013 and one in 2014. I could definitely see the deal being a 2013 6th and a 2014 4th/5th conditional type. That's not quite 4th round value, but it's very close. Oakland does not have a 5th rounder this year (we already have it) and giving a 4th straight up for Flynn would be tough for them to swallow given how good the 4th round is looking this year.
Remember too that Schneider and McKenzie are old pals that worked together as peers for many years. Wouldn't be surprised if John Schneider cut McKenzie a bit of a sweetheart deal here, especially since the Raiders seem to be the only serious suitor remaining at this point.