Mets general manager Sandy Alderson chose the happy occasion of Mike Piazza and Ken Griffey Jr.’s Hall of Fame news conference on Thursday to make his first public appearance since the team revealed last month that he is battling an undisclosed form of cancer.

Alderson, who said he has been in the office “virtually every day,” showed he still has his sense of humor as he joked about his last public appearance — when he collapsed at the Mets’ post-World Series news conference on Nov. 4.

Alderson also showed his usual feistiness when quizzed about the Mets’ continuing reluctance to re-sign slugger Yoenis Cespedes and the popular — and hard to dispute — sentiment that the club is not willing to spend like a big-market team despite coming off a World Series trip.

“Our payroll at the end of 2014 was $85 million, $86 million all-in,” Alderson said. “I would suspect this year we’ll end up at $115 or so, or maybe higher than that, $120. That’s a $35-million increase in just two years. So the idea that we’re not investing in the team I think is really misplaced, and sort of tied up in the populism involving Cespedes.”

Alderson understands that Cespedes is popular among Mets fans because he performed like a Hall of Famer after he was acquired at the July 31 trade deadline. But the Mets haven’t been willing to entertain giving Cespedes the lucrative long-term contract he is seeking.

“Look, we know that Cespedes was instrumental to us getting to the postseason,” Alderson said. “We know Daniel Murphy was instrumental in us getting to the World Series. But I think along the way we learned a few things about ourselves, about the team, and I think the way we approached the offseason, we put some of those lessons into play.

“It’s not as if we’re not looking to improve the team, and if possible, in significant ways. But it has to make some sense in terms of how these pieces all fit. And even if you go back to the trade deadline, we were trying in many ways to fit a square peg in a round hole.”

Thus, the Mets appear to be content to head into 2016 without Murphy, who was introduced as the newest member of the Nationals on Thursday, and Cespedes. That’s their No. 3 and 4 hitters from the postseason.

One reason the Mets aren’t keen on re-signing Cespedes — other than the dollars, of course — is that he would have to play centerfield for at least the first two years of his contract. That may have worked short-term, Alderson said, but isn’t his favorite recipe over 162 games.

“For two months or three months, it may make sense,” Alderson said. “For five years or six years, it doesn’t make a lot of sense to try to do that. We had the right fit [when the Mets acquired Cespedes at the trade deadline]. If we had the right, healthy player in the right position, it might be a very different story for us. This isn’t about inching up on team improvement. This is about trying to be . . . thoughtful about it, but also realistic. Trying to improve the team in ways that we can.”

As for his own health, the 68-year-old Alderson said: “I feel good. The treatments are going well, so I’m very much encouraged.”

Mets general manager Sandy Alderson chose the happy occasion of Mike Piazza and Ken Griffey Jr.’s Hall of Fame news conference on Thursday to make his first public appearance since the team revealed he was battling an undisclosed form of cancer last month.

Alderson, who said he has been in the office “virtually every day,” showed he still has his sense of humor as he joked about his last public appearance — when he collapsed at the Mets’ post-World Series news conference on Nov. 4.

Alderson also showed his usual feistiness when quizzed about the Mets’ continuing reluctance to re-sign slugger Yoenis Cespedes and the popular — and hard to dispute — sentiment that the club is not willing to spend like a big-market team despite coming off a World Series trip.

“Our payroll at the end of 2014 was $85 million, $86 million all-in,” Alderson said. “I would suspect this year we’ll end up at $115 [million] or so, or maybe higher than that, $120 . That’s a $35-million increase in just two years. So the idea that we’re not investing in the team I think is really misplaced, and sort of tied up in the populism involving Cespedes.”

Alderson understands that Cespedes is popular among Mets fans because he performed like a Hall of Famer after he was acquired at the July 31 trade deadline. But the Mets haven’t been willing to entertain giving Cespedes the lucrative, long-term contract he is seeking.

“Look, we know that Cespedes was instrumental to us getting to the postseason,” Alderson said. “We know Daniel Murphy was instrumental in us getting to the World Series. But I think along the way we learned a few things about ourselves, about the team, and I think the way we approached the offseason, we put some of those lessons into play.

“It’s not as if we’re not looking to improve the team, and if possible, in significant ways. But it has to make some sense in terms of how these pieces all fit. And even if you go back to the trade deadline, we were trying in many ways to fit a square peg on a round hole.”

Thus, the Mets appear to be content to head into 2016 without Murphy, who was introduced as the newest member of the Nationals on Thursday, and Cespedes. That’s their No. 3 and 4 hitters from the postseason.

One reason the Mets aren’t keen on re-signing Cespedes — other than the dollars, of course — is that he would have to play centerfield for at least the first two years of his contract. That may have worked short-term, Alderson said, but isn’t his favorite recipe over 162 games.

“For two months or three months it may make sense,” Alderson said. “For five years or six years, it doesn’t make a lot of sense to try to do that. We had the right fit [when they acquired Cespedes at the trade deadline]. If we had the right, healthy player in the right position, it might be a very different story for us. This isn’t about inching up on team improvement. This is about trying to be . . . thoughtful about it, but also realistic. Trying to improve the team in ways that way we can.”

As for his own health, the 68-year-old Alderson said: “I feel good. The treatments are going well so I’m very much encouraged.”