According to Rob Bradford at WEEI the Sox are planning on picking up Wakefield's option once back surgery has been completed. Assuming they'll continue to use him as a starter, that will fill the Red Sox rotation with Beckett, Lester, Matsuzaka, Buchholz, and Wakefield. Although they have options like Bowden in the minors, I'd expect them to add some veteran "lottery ticket" pitchers like last year such as Justin Duchscherer.
At $4 million, Wakefield still continues to be a steal. Even with the down free agent market, average starting pitchers can still pull in $10 million/year if they time their good season right, Kyle Lohse or Vincente Padilla for example. And even with the injuries and ineffectiveness down the stretch, Wakefield remains average overall. His ERA+ (which is a measure of ERA relative to league average ERA - 100 is league average) hasn't dipped below 100 since 2000.
Another big advantage of Wakefield compared to a free agent signing is the time commitment. At some point, Wakefield won't be able to pitch in the big leagues any longer. However, with the 1 year, $4 million dollar options in perpetuity, the Red Sox will never be on the hook for dead money. Although Wakefield hasn't been able to throw 200 innings since 2005, at $4 million I still think he's a steal. This isn't a huge surprise, considering Razy Jazayerli called it the worst contract ever from a player's perspective.