Well considering by your sites own disclaimer, the rating doesn't tell the whole story. There are plenty of names on that list ahead of Quin who are not quite as good or as young as Quin IMO. Especially if you consider a player such as Chung who wasn't even starting at the end of the season for his respective team.
I obviously believe he is higher then #18 & ultimately I believe he should be paid less then Manning, in the $3-4M/year range possibly. I wouldn't be surprised if someone offered him more because just as the Texans did w/ Manning, who wasn't a starter in Chicago, someone will pay a bit more for potential & youth. The difference is Quin is a starter while Manning never was for a long duration w/ the Bears.