Signing Webb will certainly come at a high cost for the Patriots. Since Webb is a restricted free agent and was extended a first-round tender, New England would have to give the Ravens a first-round pick in addition to the large contract Webb will certainly demand.
However, with the Patriots having two first-round picks thanks to a trade with the New Orleans Saints at last year's draft, head coach Bill Belichick can afford to give up one of those high picks to acquire a player to help the team win now, like Webb.
There wouldn't be much risk in the Patriots giving up a first-round pick, since Webb is such a great player.
Webb is an elite cornerback and is capable of covering any wide receiver in the NFL effectively. Last season he posted career highs with 67 tackles and five interceptions, and will only get better as a 26-year-old star.
The Patriots ranked 31st in the league last year in passing yards allowed per game, and the play of their secondary was consistently poor throughout the season. There were many injuries at the safety positions, and 2010 Pro Bowl corner Devin McCourty unexpectedly took a step back in his development last season.
Perhaps the best reason to sign Webb is that doing so would severely weaken one of the Patriots' top challengers for the AFC title.
The Ravens barely lost to the Patriots in the AFC championship game last season, and will certainly be one of the teams to beat in the conference in 2012.
Without Webb, combined with an aging Ray Lewis, the Ravens defense would be far weaker, and they likely wouldn't be able to defeat the AFC's other top teams like the Patriots or the Houston Texans with that kind of defense.
Adding an elite player to the weakest part of your defense and hurting one of your biggest competitors in the conference at the same time, make signing Webb the perfect move for the Patriots.