Who’s up for a half-off sale of Edwin Diaz?

The Mets should be.

Now, to be clear: The Mets paid $2 on the dollar for the young, impressive closer last offseason, only to see that trade quickly challenge the 1971 swap of Nolan Ryan (and others) to the Angels for Jim Fregosi as an all-time franchise bomb. So if someone is willing to pay one dollar on the dollar — half of what the Mets gave up — for the diminished asset that is Diaz, they should go for it.

An industry source confirmed an ESPN report that the Mets are open to trading Diaz, but the Mets will exercise this drastic measure only if an offer blows them away — just like with Noah Syndergaard, who struggled with his control Wednesday night, and didn’t get much support on offense or defense, as the Mets suffered a 7-2 loss to the Padres at Citi Field.

Maybe, however, the Mets need to recalibrate what it would mean to be blown away.

For sure, no one will approach the potent brew of goodies, including two top prospects and immense relief from the Robinson Cano contract, that the Mets handed over to the Mariners to land the best closer of 2018. Well-run teams figure out better ways to build a good bullpen than seriously compromising their young talent base. And that’s the most logical reason to trade Diaz now for the right offer: to rebuild that base with the confidence that Diaz’s value can be replicated by more efficient means.

Diaz owns an unseemly 4.81 ERA, and that’s after clocking six consecutive scoreless appearances of one inning apiece. It would seem that he bottomed out in a July 5 home game against the Phillies, when he entered a 2-2 game in the ninth inning and proceeded to allow four runs. That contest now goes down in history as the night rookie general manager Brodie Van Wagenen threw a chair as he berated Mickey Callaway and his coaches.

Asked whether he regards that game as a low point for Diaz, Callaway smiled and said, “I hope it was a low point.”

The truth likely stands as this: Diaz, 25 and not eligible for free agency until the 2022-23 offseason, will struggle to match his brilliant ’18 campaign, when he converted 57 saves in 61 opportunities, for the duration of his career. That doesn’t condemn him to a lifetime of mediocrity; he can fall short of last year’s bar and still provide considerable help. It does, however, make him less of a unicorn and more of a replaceable commodity.

So what would be an acceptable offer? Look at the package the Indians gave to the Yankees in 2016 for Andrew Miller, who had a contract taking him through 2018: Two high-end prospects in outfielder Clint Frazier and pitcher Justus Sheffield and two lesser, if interesting, talents in pitchers J.P. Feyereisen and Ben Heller. Let’s say an equivalent of that package plus one more top-30 prospect. Diaz is younger and has more team control than Miller was and did, whereas Miller already had exhibited his comfort level in high-profile spots when the trade went down.

Diaz’s aptitude for big moments remains in question in the wake of his midseason meltdown — that July 5 game capped a two-plus-month, 24-game stretch during which he posted a 7.94 ERA and chalked up six losses — and that has to decrease his trade value.

Callaway credited Diaz’s improved command for his recent uptick. Said the manager: “The things that were hurting him were the sliders in the zone and the fastballs right down the middle. Guys were making him pay for that. … And he’s starting to get his pitches to where he needed to get them to have success.”

Diaz, who has stood up for questions every time they have come his way, calmly said, through an interpreter, “I don’t really have a reaction [to the ESPN story]. It’s out of my control.”

In order to best control their future, the Mets need a boatload more of players. If Diaz can help bring that, even if it leaves the Mets in the red overall on the right-hander? That would represent a fruitful half-off sale.