There are a couple of things to remember about the situation with Berrian.
1. Because the cap has grown so quickly in the past couple of years, the top guy at any position will get a FAR better contract than the BEST players signed to contracts only a couple of years ago.
A perfect example is the Nate Clements in SF who signed the 8 year $80 million contract this past offseason. So while he's no Champ Bailey, he's still making more than anyone else at the position.
2. You have to also figure the difference in "Bears dollars" vs. the rest of the league.
With the Bears, a player actually has a good chance at playing out his contract. Whereas Nate Clements has salaries of $9m, $10.7m, and $15.5 million in the final 3 years of his contract that he will likely never see.
I think Berrian will get (from the Bears) somewhere around $15 million guaranteed on a 5 year contract worth $30 mil. On the open market, the guaranteed money will probably be about the same, but you can tack all kinds of extra stuff at the end since it's fantasy anyway. While that may sounds like alot, it's peanuts compared to what a Marvin Harrison or Chad Johnson would get in this year with this cap.