I'm not going to do an enormous breakdown. Instead, I'm going to look at Santana's season compared to the centerpiece of the proposed trade for him: Jon Lester. Of course this is only the first year of Santana's deal, but it gives a reasonable start on estimating what to expect for the next 4-6 years from these players. Here are their 2008 numbers through today:
Santana - 32 Starts, 217 1/3 IP, 2.65 ERA, 1.17 WHIP, .237 BAA, 187/58 K/BB, 23 HR allowed, 2 CG, 1 SHO
Lester - 32 Starts, 204 1/3 IP, 3.26 ERA, 1.30 WHIP, .260 BAA, 148/65 K/BB, 14 HR allowed, 2 CG, 2 SHO
Santana has clearly had the better season, leading Lester in most significant categories. His record (14-7) has been hampered by the absolutely wretched Mets bullpen, which have blown several of Santana's leads, as well as by their lineup, which has frequently failed to provide run support.
But that only begins to tell the story. For one thing, Santana has been helped by a .289 BABIP, right about average. Lester's BABIP is .303; if Lester had a .289 BABIP his ERA and WHIP would probably be pretty close to Santana's.
Plus, let's not forget that Lester is only 24, and this is his first full season in the rotation - his first Major League season, in fact, that he didn't lose part of to dealing with cancer. Previous to 2008 Lester had accumulated just one full season's worth of service time. Santana, meanwhile, is 29 and in his 8th full season. Lester is still young enough to be developing, especially after losing so much time to his fight with cancer. Give him another 5 years of seasoning (making him 29 like Santana is now) and Lester could be producing Santana's 2008 numbers.
And one more thing: the Mets are paying Santana $19 million for 2008; the Red Sox are paying Lester $421,500. Is Santana's performance $18.5 million more valuable than Lester's? Not even close.
Even at face value, The Red Sox did better with Lester at his salary than they would have with Santana at his salary; that extra $18.5 million allowed the Red Sox to go out and pick up some key additions to help them on the playoff drive (Paul Byrd, Mark Kotsay). Overall, the Red Sox have a very strong Top 3 for their rotation (Beckett/Matsuzaka/Lester) that - and here's the key - are ALL locked up for at least 2 more seasons (Lester & Matsuzaka for 4, Beckett for 2).
And here's another funny little note: in 2009, Santana will earn $20 million. Beckett, Matsuzaka and Lester will earn $19 million combined. Toss in Masterson and Buchholz (if you wanted to assumed they claimed the #4 and #5 rotation spots) and the entire 2009 Sox rotation could cost what Santana alone will cost the Mets.
Plus, the Sox are headed back to the playoffs. Unless the Mets pull off a 2007-Phillies-like turnaround, they won't be.
And would the Sox be heading back to the playoffs at all if they'd done the trade? Yes, they'd replace Lester's performance with Santana's, but they would also NOT have had Justin Masterson, who gave them several strong starts and then saved their weak bullpen, OR Jed Lowrie, who has played his way into the starting SS role (the Sox plan to shop Lugo in the offseason). Even Crisp has been damned valuable, platooning with Ellsbury, playing exceptional defense and even hitting pretty well in the 2nd half. Purely in terms of playing value, losing those three players would more than have negated the value of Santana-over-Lester.
Point: Epstein. It's things like this that make the Sox so anxious to keep him.