Matt Swarz, Hardball Times Annual 2011. His number was just shy of $9M. I have reproduced the "study" (RE one fairly simple SQL query) in the past and came within a quarter million.
The main thing people fail to realize when thinking about this is that we need to look at the actual number of WAR produced on the FA contracts. You don't pay for past WARz, you pay for the future WARz produced under contract.
For example, if a 3 WAR player in 2009 and signs a 2 year FA contract before the 2010 season, we sum his 2010 and 2011 production and see how that compares to the $ he was paid. Rinse and repeat for all FA contracts and you get your league wide #s. Doing this by hand is obviously a colossal pain in the ass.
With all the new money in baseball I'm guessing we would find this number is actually north of $10M this offseason.