By Dan McSwain

As a third billionaire jockeys to attract one or more NFL teams to Los Angeles, San Diego Mayor Kevin Faulconer has formed a task force to study a new Chargers stadium in Mission Valley or downtown.

Such hubbub has me wondering if there is a decent business case for building one in San Diego.

Certainly, keeping a local team would be nice. Go Chargers!

Before I dive in, it’s worth remembering that governments build worthy projects all the time that don’t “pencil out.” Parks leap to mind.

Through the political process, the public very well might decide it wants to get involved, for a host of nonfinancial reasons. Another thing: The Chargers have declined to release relevant financial information. So my numbers, or anybody else’s, are necessarily estimates.

Let’s start with what we do know: The Spanos family, which owns the Chargers, wants a new stadium costing about $1 billion.

On the bright side, interest rates are low. The annual payment would be about $80 million, assuming a 20-year loan at 5 percent interest.

We can assume a similar “cost” for a cash investment. If I had a cool billion sitting around, I’d want at least 5 percent.

Yet the good news ends there, businesswise.

In a 2004 presentation, the Chargers estimated that a new stadium at the Qualcomm site in Mission Valley would boost the team’s “local revenue” by $15 million a year.

A fresh estimate by John Vrooman, a sports economist at Vanderbilt University, put the gross increase at $50 million (some would indirectly go to players via league revenue sharing).

At $15 million or $50 million, either figure is a long way from covering $80 million in new costs, let alone boosting profits. This may explain why the Spanos family hasn’t simply built a stadium itself by now, after 13 years of occasional pleas for public help.

“Your calculations do demonstrate the severe and very practical limitations we face in San Diego with regard to private investment on a new stadium,” said team spokesman Mark Fabiani, declining further comment.

My take-away: The team’s deal at Qualcomm is too good to abandon without hefty public subsidies.

Under NFL rules, the league’s 32 teams divide equally the revenue from TV contracts, national licensing and ticket sales for standard seats. Lest we feel sorry for them, the split worked out to $170 million for each owner in 2013, according to Forbes annual estimates.

But charges for luxury suites, club seats and local licensing deals are considered local revenues and flow to individual teams.

This very healthy number, which Forbes put at $93 million in 2013 for the Chargers, should top $100 million this year, Vrooman estimates.

After all, Qualcomm Stadium was upgraded in 1997 with 113 suites and 7,800 club seats. So while a new stadium could boost local revenue to $150 million, playing at Qualcomm clearly is a viable business strategy.

By the way, local revenue could soar to $300 million in Los Angeles. San Diego fans are right to worry.

Of course, sustaining a business requires a focus on profits, not necessarily revenues. Under the NFL’s salary cap formula, players receive 40 percent of local revenues and 55 percent of national TV contracts.

The formula skews profits toward teams in newer stadiums with more or higher-priced luxury seats.

Forbes ranked the Chargers’ market value in the bottom quarter of the NFL with an estimated 2013 profit of $39 million, while Vrooman reckons it is $75 million this year.

From the Spanos family’s perspective, either figure looks a whole lot better with $25 million a year from a new stadium.

Bear in mind, all these projections assume that fans and corporate sponsors will pay higher prices to fund a fancier stadium.

This seems plausible. San Francisco’s $1.2 billion, privately financed stadium, which opened last year, is considered a business success.

Yet there may be wiggle room in the Chargers’ $1 billion wish list.

In 2004, the team said a new stadium in Mission Valley would cost just $400 million. The federal inflation index for nonresidential construction suggests that same stadium would cost no more than $600 million today.

“It’s sometimes called gold plating,” said Bruce Johnson, sports economist at Centre College in Danville, Ky., referring to the tendency of stadiums to get fancier over time, especially when public funding is involved. “If the city buys it for us, we’d like the exploding scoreboard.”

This brings us back to who might pay for a $1 billion stadium.

Vrooman estimates the team could raise $300 million from fans, by selling “personal seat licenses,” or advance payments that secure a right to buy tickets. And the NFL might lend the team $200 million.

This covers half of the Chargers’ $1 billion estimate. In Viking-crazy Minnesota, the public split the cost 50-50 with the team.

Yet cities rarely get a cut of stadium revenues. Remember that hypothetical $50 million boost to Chargers local revenue? Repaying the NFL over 20 years could cost $16 million or more per year.

If the Chargers had to split the remaining $34 million with the city, leaving Qualcomm would become a riskier business proposition. And the city’s $17 million share wouldn’t cover $40 million in annual loan payments on a $500 million debt.

A decade ago, the team proposed redeveloping Qualcomm.

Last week Gary London, a veteran commercial real estate adviser, estimated the site’s 166 acres could have a market value of about $200 million to a developer — but the true figure would vary widely, depending on how many condos, offices and stores were permitted.

In 2004, the Chargers estimated the development would generate $16 million a year in taxes for the city.

That’s worth a whopping $816 million to the city in today’s dollars, assuming a 4 percent discount rate and 2 percent annual growth in tax revenues, according to my “perpetual growth” value calculator.

Schemes like that can make these projects seem more palatable, but they really are misleading. If you think about it, ongoing tax revenue is an argument for developing the entire site — without taking up land with a stadium, which typically pays no property tax.

Should the public give the Mission Valley land to the Chargers for development, and let them build a stadium downtown? That scenario arguably leaves a $300 million funding gap, versus simply waving goodbye to the team when its lease expires in 2020.

In San Diego County, such a gap works out to $300 per household (or $500, if you include the land’s value). Put another way, that’s $24 to $40 per year for each household, using our 20-year loan example.

It turns out that economists for years have tried to quantify how the public values projects with no tangible payback, such as open space or, you guessed it, sports teams.

Johnson, the Centre College professor, is an acknowledged expert.

“It’s hard to find cases where the intangible benefits are big enough the justify the subsidies that go to these things,” Johnson said. “People say they really like sports. They like civic pride and the sense of community, but they are not willing to pay $500 million for a new stadium.”

San Diego’s willingness is a huge question mark.

A 2002 study suggested that Minnesotans were willing to pay $530 per household toward the Vikings $1 billion stadium.

However, a 2005 study indicated people in Jacksonville, Fla., would pay just $84 to $124 per household to keep the Jaguars from leaving. And support crumbles when surveys compare stadium funding with priorities like schools or roads.

Yet weak public support hasn’t stopped lawmakers from subsidizing projects, partly because of heavy lobbying from industries that benefit. And politicians who promote projects are often out of office when the bills come due.

Fabiani, the Chargers spokesman, declined to tell me if the team has measured local public appetite for stadium funding.

He said the team regularly conducts surveys of various kinds but has never disclosed results.

With any luck, the mayor’s task force will fill in all the blanks this year.