(FILES) This file photo taken on December 28, 2016 shows the logo of US electronic commerce and cloud computing company Amazon in Vertou, France. Amazon said January 18, 2018 it had narrowed to 20 its options for a second headquarters for the sprawling technology and lifestyle company headed by Jeff Bezos, the world's richest individual. After 238 cities from North America submitted bids, Amazon announced its short list included three in the vicinity of the US capital Washington, and the Canadian city of Toronto. / AFP PHOTO / LOIC VENANCELOIC VENANCE/AFP/Getty Images (Loic Venance/AFP/Getty Images)

HOW MUCH is too much for cities and states to dangle as incentives for the prize of capturing Amazon's gargantuan second headquarters, a complex that would eventually constitute far more than a Pentagon's worth of office space and roughly two Pentagons' worth of employees? That's a pressing question, and one freighted with long-term consequences for the Washington region, home to three of the 20 finalists — the District, Montgomery County and Northern Virginia — on Amazon's shortlist of contenders.

Granted, it would be, well, seriously cool to win what easily qualifies as among the biggest economic development jackpots in decades, a venture that Amazon says would eventually mean 50,000 employees and some $5 billion worth of investment. But officials hoping to burnish their legacy should proceed with caution, with their eyes at least as wide-open as their wallets. (Disclosure: The Post is owned by Amazon founder and chief executive Jeffrey P. Bezos.)

As former Indiana governor Mitch Daniels, the president of Purdue University, wrote in these pages recently: "Nothing in public life is more dangerous to the public interest than politicians chasing 'jobs' with the people's checkbook." Those politicians, Mr. Daniels noted, will reap the glory of a winning bid but "won't be around when the bills come due."

To make the case briefly: Landing a fish as big as Amazon would entail massive benefits but also real costs and risks for the winner. So incentives should be calculated according to rational and transparent metrics. And, in the Washington area's case, wouldn't it be smart if the three contestants managed to coordinate their offers before a corporate-welfare arms race goes nuclear?

Already, Maryland Gov. Larry Hogan, a Republican just stung by the announced departure of Discovery Communications from Silver Spring, has formulated a package of goodies worth $5 billion . That's less than New Jersey's $7 billion but in the same expansive ballpark. At $100,000 per newly created job by the online retailing behemoth, it is a head-spinning proposal and, with reason, has prompted some state lawmakers to raise questions.

Before Virginia or the District matches or tops Mr. Hogan's bid, all three might consider a modest proposal. Given that the region, not just the winning locality, would reap the blessings of a new Amazon headquarters — jobs, growth and prestige, to name a few — wouldn't the region be wise to collaborate on a joint, transparent and publicly vetted incentive package before the winner is announced?

Granted, that would require that officials devise a cost-sharing formula, because Amazon's costs and benefits would accrue disproportionately to the winning state and locality. Still, it would recognize the reality that boundaries in this region are porous and its localities mutually dependent. A united front might strengthen all three bids.