With the Phillies finally admitting that they’re not going anywhere fast, Ruben Amaro is talking to teams about Cliff Lee. The Red Sox are reportedly showing the most interest, and despite the fact that Boston is on Lee’s 21 team no-trade list, those are almost always negotiable, and Lee would probably rather play for a winner than an aging team with no clear path to get back on track. So, in a market that has been mostly littered with back-end starters and bullpen pieces, there’s finally a bonafide ace in play.

Make no mistake, Cliff Lee is an ace. Over the last three calendar years, Lee has thrown 660 innings and posted +16.4 WAR, coming in behind only Justin Verlander, Clayton Kershaw, and Felix Hernandez. He’s not a low FIP/high ERA guy either, as his RA9-WAR is +16.5. No matter how you evaluate pitchers, Cliff Lee is one of the best pitchers in the game. He may not be the hardest thrower in the world, but his command and overall repertoire allow him to dominate opponents just the same as if he throw 100 mph.

But acquiring Cliff Lee, Bonafide Ace, will come at a very high cost, and depending on what Philadelphia is asking for, the Red Sox might very well be better off walking away.

As Jon Heyman noted yesterday, the Phillies aren’t just looking to move Lee’s contract. They want serious talent in return too.

“He’s telling people it’ll take you three or four best prospects, plus you’d have to take all the money,” one competing executive said of Phillies GM Ruben Amaro.

There are times when it makes sense to trade your three or four best prospects to upgrade your roster. There are times when it makes sense to take on high priced contracts to acquire premium talent. However, as good as Cliff Lee is, the combined cost of both of those things together far outstrips Lee’s actual value.

Let’s start with what a contender could expect from Lee going forward. Over those last three calendar years, Lee has given up runs at 77 percent of the league average. If he was traded to the American League and maintained his three year average, that would translate into a 3.10 ERA. That might be a little optimistic, given that the three year time period gives equal weight to his amazing 2011 performance as it does to his more recent, slightly less amazing performances, which is why both ZIPS and Steamer forecast a 3.25 ERA going forward in the National League, translating into something closer to a 3.50 ERA in the American League.

But, because the specific number doesn’t matter too much, we’ll just pick 3.25 as his expected rest-of-season ERA, splitting the difference between his recent performance and his forecasts, in case you think they’re too negative. In Boston, Lee would replace some combination of Brandon Workman (4.61 ERA rest-of-season forecast), Allan Webster (5.01), or if Clay Buchholz ever gets healthy, Felix Doubront (4.18). Clearly, Lee would be a significant upgrade for the Sox rotation.

But we’re still only talking about a couple of months of regular season baseball, and even the best players don’t really make dramatic differences over that kind of time period. For instance, swapping out Workman for Lee would result in a difference of about 1.36 runs per nine innings. However, the Red Sox only have 55 regular season games left to play, so you’re looking at 11 starts before the season ends. 11 starts at a little over seven innings apiece gives us roughly 80 innings, so then we can just do the math. (1.36/9)*80 = 12. Replacing Brandon Workman with Cliff Lee for the final two months of the season would save the Red Sox something like 12 runs.

Depending on how those runs are distributed, that’s an extra win, or maybe two if things break right. Those are absurdly important wins, given that the Red Sox are in a dog fight with the Rays for the American League East championship, but we’re still talking about a regular season upgrade on the magnitude of one or two wins. Right now, Cool Standings gives the Rays and Red Sox both about between a 45-50% chance of winning the division, with the loser very likely to end up in the Wild Card game. Give the Red Sox an extra win or two, and and it pushes their odds of winning the division up closer to 55-60%.

The idea that acquiring Cliff Lee guarantees the Red Sox the division title, or even makes them prohibitive favorites, simply isn’t true. He makes them better, and gives them a better shot at skipping the Wild Card game, but the calculus is simply not Acquire Lee/Have Parade. Even if they trade for Cliff Lee, there’s going to be something like a 4-in-10 chance that the Red Sox end up playing one game with their season on the line against another very good team, and even with Cliff Lee, they could easily lose that game and have their season end.

And if they had given up multiple premium prospects — Ken Rosenthal tossed out a suggestion of Xander Bogaerts and Allan Webster this morning — that result would be a total disaster. At that point, not only would they have to watch Bogaerts likely turn into a star for the Phillies, their ability to improve their roster for 2014 and beyond would be severely compromised.

This isn’t the only outcome, possible, of course, but one cannot simply note that acquiring Lee could lead to a World Series parade without noting that it could also lead to a disappointing early exit and a significantly weakened future. In fact, that outcome is far more likely, and having Lee’s salary on the books — and not having guys like Bogaerst and Webster around to provide low cost performance — could put the Red Sox right back where they found themselves last year.

Lee’s contract calls for him to earn $25 million in each of the next two seasons, and then there’s a team option for $27.5 million in 2016 that comes with an odious $12.5 million buyout, meaning that the actual decision will be whether or not Lee is a $15 million pitcher at age-37. Not even including the 2013 dollars a team would be taking on, Lee would either cost $62.5 million for the next two seasons or $77.5 million for the next three.

While Rosenthal notes that the Red Sox cleared a lot of money off the books in the Adrian Gonzalez trade last August, it should be noted that the Red Sox re-spent a good chunk of that money in putting together their 2013 team, bringing in Ryan Dempster, Shane Victorino, Stephen Drew, Mike Napoli, Jonny Gomes, Koji Uehara, and David Ross. That’s what payroll flexibility allowed them to buy, and those guys have combined for +9.5 WAR. Having a balanced roster of quality contributors is one of the primary reasons that the Red Sox are back in the playoff race.

Stick Lee’s $25 salary in the mix for 2014, and you have to account for the players that can no longer be signed as free agents now that he’s taking up a big chunk of the budget. And Lee just isn’t likely to keep outperforming what the Red Sox could get with the money they’d be agreeing to take on. He’ll be 35 next year, and his skills are already showing some signs of erosion.

Over the last three years, his strikeout rate has gone from 26% to 24% to 23%, even as the league average strikeout rate has gone up during that time. While he’s not known as a guy who relies on his velocity, his average fastball has slipped from 92 to 91. He’s still an ace, but even aces have shelf lives, and he’s unlikely to keep performing at his current level for too much longer. Right now, Cliff Lee is worth $25 million per year. He might even be worth that next year. But in 2015, the Red Sox would probably be better off with whatever they could buy in free agency than paying a 36-year-old Lee hoping he’s still an All-Star. And that 2016 option looks particularly scary, as it’s extremely unlikely that Boston would be better off paying Lee $27.5 million at age-37 than they would be by giving that money to other players. The alternative is paying him $12.5 million to go away, which would raise the cost of the 2014/2015 years to over $31 million apiece.

For that kind of money, the Red Sox could sign a half dozen players that collectively far outstrip whatever he could provide by himself. Or they could throw a portion of it at Matt Garza this winter, and get a pitcher that projects to be similarly valuable over the next few seasons — once you factor in their respective ages — only $77 million probably gets you five years of Garza instead of three years of Lee.

And, of course, they’d still have whatever prospects they gave up to to get Lee, or the opportunity to turn those prospects into more valuable players this off-season. For instance, Rosenthal’s suggested Bogaerts/Webster package would be a pretty good starting spot to get the Marlins to reevaluate their stance on not trading Giancarlo Stanton. Even if you don’t trust prospects and think that the Red Sox should be going all in to try and win, it’s not unreasonable to think that Bogaerts, Webster, and $77 million in future commitments gets you pretty darn close to acquiring both Stanton and Garza this winter.

Of course, making moves this winter doesn’t really help the Red Sox in October, and Rosenthal’s primary point appears to be that teams should be more concerned with trying to win a ring than keep an impressive stockpile of talent on hand. However, you can’t do the former without doing the latter. Teams win the World Series because of the impressive collections of talents they’ve acquired and retained. Acquiring Lee for the rumored cost would improve the Red Sox odds of winning the 2013 World Series, but decrease their odds of winning the next three. The decision isn’t “win the World Series or not”, but whether or not an upgrade now really improves your odds of winning this World Series enough to reduce your odds of winning future World Series.

Rosenthal points to the Hanley Ramirez trade as an example of why the Red Sox shouldn’t be afraid to go for it, but Josh Beckett was 26 when they got him from the Marlins. He provided both immediate value and long term value, as a quality starter who would make it more likely that they would win the World Series during the years they controlled his rights. Josh Beckett made $2.5 million during the season he was acquired by the Red Sox, then $4.3 million the next year, then re-signed with Boston for $30 million over three more years. Beckett made less during his first five years in Boston than Lee will make over the next two.

Yeah, there’s more money in baseball now than there ever has been, and the Red Sox can afford Cliff Lee, but that doesn’t mean they should stop counting the costs of of his acquisition. If the asking price was just to take on the money and give up some decent low level prospects, then yes, they should go for it. If the asking price was to give up premium talent while the Phillies subsidized his salary for the next two seasons so that they got a quality starter at below market prices and maintained their financial flexibility to still go out and add talent in free agency, then that might even be worth considering, though probably still wouldn’t be worth surrendering a player like Bogaerts.

But to take on all of Lee’s money and give up elite talents? That’s the kind of franchise crippling maneuver that every team in baseball — rich or poor — should be avoiding. Every team isn’t trying to emulate the Rays because they like being lauded for being smart; every team is trying to be the Rays because building around highly talented low cost players is the best way to build a sustainable winner. If you give up both your best talent and your financial flexibility in one move to acquire one aging pitcher, you will soon find yourself in the same position as the franchise that is currently owns Cliff Lee.

Lee makes a lot of sense for the Red Sox, and acquiring him would give them a better chance to win the World Series this year. Just realize that adding Lee would push their WS odds from something like 10% to 15%. He’s a piece, a helpful piece, but with or without Lee, a World Series title is unlikely. Mortgaging the future to chase unlikely wishes is how you end up in last place with few hopes and no way out. The Red Sox just got out of that mess last year. It is not time to go back.