DID the Mets overpay for Billy Wagner? It all depends on what your definition of “overpay” is. If your roof is leaking, and there’s a guy who knows how to stop it available for one price, and another guy who “might” stop it available for a few bucks less, are you overpaying the competent guy? Or are you simply making sure the water stays out of your living room?

If “Good Night and Good Luck” is showing at one theater for nine bucks, and a Pauly Shore double-feature is playing across the street for $2, are you overpaying to see Murrow take out McCarthy, or are you simply sparing your brain cells?

“We had a very big need to fill,” Mets general manager Omar Minaya said yesterday.

Minaya was being terribly kind in that description. The fact is, the Mets needed to get a closer, a good one, a reliable one, or else anything else they did this offseason was completely meaningless. They needed to target the best available man for the job and do everything short of kidnapping him to make sure he agreed to play at Shea this summer.

Wagner was the best available man for the job, and the Mets didn’t have to kidnap him. They did have to take him on a white-collar tour of the Westchester and Connecticut suburbs. They did have Tom Glavine and his wife, Christine, serve as personal tour guides. They even had a fellow native Virginian, Jimmy Plummer, from the marketing department, spend an hour in Minaya’s office, talking about shared acquaintances.

“He seemed awfully comfortable to me,” Plummer said of Wagner.

If he wasn’t, then the Mets would have had to import some instant comfort, maybe buy the Wagners a new set of Laura Ashley comforters, maybe cook up some comfort food, maybe pour a few glasses of Southern Comfort, or hire Elton John to sing “Country Comfort.” Whatever it took. The $43 million and the no-trade clause that sealed the deal, they were almost incidental.

The Mets had to make Billy Wagner damned comfortable.

They needed his signature on a contract to make them comfortable.

There was no alternative.

“We had a few missteps in the bullpen last year,” COO Jeff Wilpon said yesterday, and as the sentence rolled out of his mouth you could see him wince, the way every Mets fan in creation winced the past few years when talk turned to the back end of the team’s bullpen.

Let’s be honest: The Mets haven’t had a confidence-inspiring closer since Randy Myers’ one standout season with the team in 1988. John Franco was a one-man amusement-park ride. Armando Benitez was a big-moment calamity waiting to happen. Braden Looper kept Maalox’s New York-area sales brisk.

“When you have a first-rate closer, you are in the other team’s head right away because they know they have to get a lead in eight innings,” Minaya said. “But if you have a lead in the ninth and wind up losing a game you had won, that can stay with you for a day or two.”

Or longer. In so many ways, the Mets never really recovered from Opening Day last year, when Looper inherited a two-run lead in Cincinnati and gave up home runs to Adam Dunn and Joe Randa that wasted Pedro Martinez’s Mets debut.

Wilpon saw that game on television back in New York and felt physically ill watching it unfold. He wasn’t alone.

There were other Looper bloopers – one terrible Sunday night in The Bronx, one gruesome Friday evening in Pittsburgh – but Opening Day cast a pall over everything else. From that moment on, there wasn’t a Mets fan – or a Mets teammate – who believed there was any such thing as a safe ninth-inning lead.

You can’t win championships that way. Hell, you can barely get out of bed every morning knowing the adventures that lay ahead. The Mets have too much riding on 2006 to entrust ninth innings to a crapshoot. You think $43 million over four years is overpaying? For some teams, it might’ve been.

For the Mets, it was simply the cost of doing business.

michael.vaccaro@nypost.com

Closing the gap

With the acquisition of closer Billy Wagner, the Mets continued to improve their team this offseason while the Yankees virtually have been standing pat.

Here’s a look at the teams’ projected lineups, with newcomers in bold.

METS Pos. YANKEES

Carlos Delgado 1B Jason Giambi

Kaz Matsui 2B Robinson Cano

Jose Reyes SS Derek Jeter

David Wright 3B Alex Rodriguez

Cliff Floyd LF Hideki Matsui

Carlos Beltran CF Bubba Crosby

Victor Diaz RF Gary Sheffield

Ramon Hernandez C Jorge Posada

Pedro Martinez SP Randy Johnson

Tom Glavine SP Mike Mussina

Kris Benson SP Carl Pavano

Steve Trachsel SP Chien-Ming Wang

Victor Zambrano SP Aaron Small

Billy Wagner CL Mariano Rivera