I'll give you a number of factors that help a pitcher while switching leagues, specifically to the NL West:
Bigger parks, weaker lineups, pitchers hit, the Mets.
Even if they get Holliday and extend V-Mart, the Sox should still have enough money after '10 to go after Mauer with Lowell's, Tek's and Papi's contracts expiring.
This is where Yankee fan X comes in and says:
"But...but...but.....he leads the league in saves!!!!"
Then we all laugh and prove how little does a stat like saves mean to the actual value of a closer on any given year.