Martin and Fyfe are worth 1.5+ million a season range. Hill is in a different market to those players all together.Saints are offering a deal that puts Brad Hill in the top 2.3% of all players, not enough to field 18 players in the number at that level.
Plus he has two years to go. That's the value they've put on him. That is two top ten picks.
You wouldn't shake loose the likes of Franklin, Martin, Fyfe etc from their clubs without a sizable offer, St Kilda have valued him in that area.
Keep in Mind St Kilda has plenty of cap space hence can over pay Hill, to entice him to join the club.