At Jason Varitek’s peak, he was a top-five catcher, an offensive force who was just as valuable behind the plate as he was in the locker room.

But offensively, that peak is at least three years gone. The Red Sox would be making a mistake to pay him like the player he once was, when similar players around the league make half as much as Varitek reportedly wants.

Varitek and his agent, Scott Boras, initially wanted a four-year deal worth $40 million, similar to the deal Varitek just completed. In 2008, Varitek was the league’s third-highest paid catcher, behind Jorge Posada and Ivan Rodriguez of the Yankees.

As the offseason has worn on, however, no other team has seemed interested in signing the 36-year-old Varitek to a long-term deal, and it is thought that Varitek and the Red Sox are now discussing a shorter contract.

But even at two years, and close to $20 million, it looks like Varitek would be a bad investment. Examining the statistics and salaries for 2008 and 2009, the Red Sox would be paying twice as much as other teams pay to catchers with equivalent production — and options exist on the free-agent market who could easily  replicate Varitek’s production, if not his clubhouse influence.

At this point in his career, Varitek is a slightly below-average starter at his position, and signing him to a contract that pays him like a top-five player would be unlike the John Henry Red Sox, who have demonstrated over the years that they will not overpay for sentimental reasons.

Teams got, on average, 75 runs, 15 home runs, 73 RBI, and a .258 average over 162 games from the catching position in 2008. That, however, is a  misleading statistic, as the wear and tear that catchers take over the season means that most play far fewer than 162 games — the league leader, the Dodgers’ Russell Martin, played 155, and only seven catchers played more than 140 games.

It is perhaps more appropriate to compare Varitek to a group of the top 30 catchers by games played, which puts him up against the primary catcher for each team.

Among this group, Varitek’s value becomes clearer: At this point in his career, he is a distinctly average catcher, better than just less than half the primary catchers in the majors.

The typical primary catcher appeared in 119 games, with 394 at-bats. He hit for a .259 batting average, with a .329 on-base percentage, and a .403 slugging percentage. He scored 47 runs, hit 11 home runs, and amassed 53 RBI. He stole two bases.

Varitek’s numbers are slightly below-average for that group in almost every regard. Varitek, in 131 games, provided 37 runs, 13 home runs, 42 RBI, and a .220 average.

He has good plate discipline, and so his 52 walks helped balance off his poor average and allowed him to compile a .313 on-base percentage, but both that and his .359 slugging percentage were below the average for this group. His 122 strikeouts were almost twice as many as the average primary catcher.

Varitek’s .996 fielding percentage ranked him among the best in the league at avoiding errors, though his ability to throw out runners — 56 successful steals, 16 runners caught stealing — would rank him below average among primary catchers.

Many have argued that this was a bad year for Varitek, and it certainly was. But even using the averages of his last three years — a .237 average, .335 on-base percentage, 47 runs, 14 home runs, and 55 RBI — Varitek is still no better than an average catcher, and does not figure to improve with age.

Famed  baseball analyst (and Red Sox employee) Bill James projects extremely similar numbers for Varitek in 2009, with a slight bump in batting average.

So who matches up with Varitek, and what are they worth?

The most comparable players in 2008 were Royals’ catcher John Buck, Toronto catcher Rod Barajas, the Phillies’ Carlos Ruiz, new Tiger Gerald Laird, and the Mets’ Brian Schneider, who had a similar pace to Varitek despite 100 fewer at-bats.

In this group, one statistic leaps out: Varitek’s salary demands are dramatically higher than what every one of his “average” peers earned this year.

Buck and Barajas are perhaps the closest comparisons statistically. Barajas, a seven-year veteran, earned $1.2 million in 2008 and will make $2.5 million in 2009. Buck, a three-year veteran who is not yet eligible for free agency, made $2.2 million.

Ruiz is just coming off his rookie year and makes just over the league minimum, Schneider is locked up by the Mets at $4.9 million, and Laird, a player the Red Sox tried to acquire this offseason, earned $1.6 million.

The other interesting Varitek comparable is 37-year-old Ivan Rodriguez, who is also on the free-agent market after finishing up a five-year deal with the Yankees and the Tigers. Rodriguez, considered one of the best defensive catchers of all time, and had a year very similar to Varitek’s, hitting for less power but with a higher average.

But more important, Rodriguez was the highest-paid catcher in baseball last year at $13 million, trailed by Varitek and Posada. Not coincidentally, Rodriguez is also a Scott Boras client. And Rodriguez is drawing little interest on the free-agent market.

Perhaps the best free-agent Varitek clone, for the money? Toronto’s Gregg Zaun. In only 245 at-bats, the 37-year-old Zaun scored 29 runs, hit 6 home runs, and drove in 30, hitting .237 and walking enough to achieve a .340 on-base percentage. His .359 slugging percentage equaled Varitek’s, and his most recent full seasons closely mirror Varitek’s.

The allure? His likely price. The switch-hitting Zaun made $3.75 million in 2008, before the Blue Jays declined to offer him arbitration, making him a free agent.

The Boston Globe reported yesterday that the Red Sox and Zaun’s agent have talked this offseason, and Zaun said he would love to come to Boston.

The Red Sox also recently signed San Diego’s Josh Bard to a one-year deal, although Bard is seen by the team as a backup or a platoon player.

Of course, none of this takes into account Varitek’s unmatched preparation, his clubhouse leadership, his veteran presence or his meaning to the fan base. He is the team captain, and the C on his jersey was hard-earned over 11 years in Boston. While less quantifiable, that is certainly worth something in dollar terms, and both Boras and the Red Sox know this.

What, then, is Varitek worth? By the numbers, veteran players producing at his level were generally paid between $2 million to $5 million by their teams in 2008, with the exception of the Yankees’ Rodriguez.

If Varitek’s price were to drop that low, the Red Sox would probably be happy to bring him back for at least two more years. But if Varitek and Boras stick to their initial demands, the Red Sox will probably go another way, and end up with the same production for half the cost.