The only wrench in that plan could be the state of baseball revenues down the road. “As revenues grow, salaries grow more or less proportionately,” says Andrew Zimbalist, a professor of economics at Smith College. “Baseball revenues, in my view—and revenues of all the team sports—have gone through a very rapid period of growth, and I don’t see that growth continuing.”

Zimbalist believes changes in telecommunications technology and the ways in which viewers consume games are likely to put pressure on sports marketing rights. In other words, the period of explosive growth in lucrative television contracts has probably come to an end. “The way the structures of the industry have changed over the past 15 years or so has been very propitious for sports television rights,” he says, “but I don’t think that will continue.”

If baseball revenues don’t grow at the pace we’ve seen in recent years, perhaps teams will be reluctant to sign on for a landmark deal. Zimbalist, for one, thinks the half-billion-dollar figure is unlikely. “I don’t see it now, and I don’t see it in five years,” he says. “And I’m not surprised that agents would throw those numbers out, because it’s in their interests to always raise expectations and always hype up the bidding for their players.”

But as A-Rod’s deal shows, sometimes a club will put up an out-of-this-world number anyway—especially if a team owner is dead set on signing a particular superstar, as was the case with then–Rangers owner Tom Hicks. Of course agents would like to point to whatever number Harper reaches as a kind of benchmark, but those who spoke with Sportsnet admit that Harper is a wild card. It will likely take another generational talent to exceed whatever figure he reaches.

Maybe the more interesting question turns out to be not whether Harper will land half a billion dollars, but what it’ll do to his star power if he gets that kind of money. It can be tricky to remember A-Rod’s persona before fans started to view him as a walking, talking pile of cash—and before his legacy was complicated by steroids. But there was a time, before he’d reached free agency, when Rodriguez enjoyed the kind of relatively uncomplicated stardom Harper is accustomed to today. “He was super approachable, friendly, co-operative. He was charismatic,” says Larry Stone, a sports columnist with the Seattle Times who was around for all but A-Rod’s first season with the Mariners. “The fans loved him.”

Tyler Kepner, a baseball writer for the New York Times who covered Rodriguez’s penultimate year with the Mariners for the Seattle Post-Intelligencer, remembers him in those days as “a pure young talent who also seemed like he really was a great guy.” But the shadow of a potential departure loomed large, Kepner says. “The issue of how much he was going to be paid in his free agency was always hovering over him.”

When Rodriguez left for Texas and eventually returned to Seattle in a Rangers uniform, the fans who’d once loved him let him have it. “It was vicious, it was constant, it was absolute,” says Stone. “It was non-stop derision. People brought fake money. Every time he came to the plate, they threw it. To this day, every time A-Rod comes back, somebody brings the fake money and throws it from the top deck so it kind of flutters to the ground.”

Of course, Harper and A-Rod are different cases. But if Harper ends up with a contract bigger than anything we’ve ever seen, it will take a special kind of poise to face the haters he’s likely to attract. That’s especially the case if the guy they call “Bam-Bam” ends up with the Yankees, Dodgers or Red Sox, the teams most likely to pay him that kind of money.

Half a billion dollars might be a ridiculous sum—“No human being is worth that kind of money,” one agent remarked—but even if it’s ridiculous, it hardly seems unfair. Harper is a special case, and with the current benchmark for average annual value amongst marquee players being what it is, it’s easy to see why he might well ask for the moon and get it.

Some purists balk at the astronomical salaries the game’s biggest stars now command. If Harper earns his payday by leaving the Nationals, he might well end up a villain in the eyes of his current fans. For now, at least, he can bask in their adoration—as he did when he hit his 100th major-league home run. Those fans demanded a curtain call, and Harper obliged, emerging from the dugout for a brief appearance, squinting in the afternoon sun as he pumped his right arm skyward. The moment was captured in a widely circulated photograph that revealed one of sport’s iconic grins; Harper looks like the hero of some movie, forever locked in triumph in the final freeze-frame shot. Funny, since his story is only just beginning.