The value of milestone baseballs has decreased significantly since Mark McGwire's single-season record 70th home run ball in 1998 fetched a whopping $3 million. The man who purchased that ball was Spawn comic book creator Todd McFarlane. Three years after his big investment, McFarlane saw Barry Bonds one-up McGwire and hit a record 73 homers. McFarlane bid $517,500 for No. 73, but the damage was done: McGwire's ball had been significantly devalued.
Matt Murphy, 22, of Queens, N.Y., came away with the ball Bonds struck for No. 756 on Tuesday night, and now has a chance to use it like a lottery ticket. Though whether Murphy will be able to fetch as much as McFarlane did for Bonds' No. 73, is unclear. "I think it's worth somewhere between $350,000-$500,000," says Brandon Steiner, founder and owner of Steiner Sports memorabilia, the most well-known collector of current-day sports memorabilia.
Brian Marren, vice president of acquisitions for Mastro Auctions, the country's largest sports auction house, estimates the ball's worth around $500,000. Mastro sold the Steve Bartman ball a few years ago for $150,000, and doesn't see why Bonds eclipsing Hank Aaron's all-time mark shouldn't go for at least a half-million dollars.
"And Bartman was a foul ball," Marren says.
Mike Heffner, president of Leland's auction house that sold Bonds' No. 73 ball to McFarlane in 2003, thinks the ball could fetch $500,000, or more.
"There's no way of really telling what it's worth," Heffner says. "And with the steroid allegations, it certainly doesn't help."
There are many factors that will contribute to the worth of the ball. Here are a few for Murphy to consider:
Where the ball lands
Most auction houses would have been out of luck if the ball had landed in the bullpen instead of the bleachers, since a fellow player most likely would return the ball to Bonds. Or there was the scenario Padres closer Trevor Hoffman suggested: If he had caught the ball, he would have auctioned it off and given the proceeds to San Diego bullpen catcher Mark Merila, who's battling brain cancer. McFarlane said Bonds' No. 72 in 2001 hit off the top of the outfield wall and bounced back onto the field. "After I bought the ball, I reminded Barry that if he had stopped there he'd have his record ball all to himself," McFarlane says. "I tell him maybe I'll bring it to the ballpark now and then and let you take a look at it."
Where the seller chooses to go
Unlike auction houses, which work with the owner of the ball and take a cut of the earnings, Steiner's company would cut a check directly to Murphy. Steiner says he'll likely then sell 2,000 lottery tickets, somewhere in the neighborhood of $400-$500 each, with one lottery winner taking home 756. The remaining 1,999 entrants are each promised a signed ball by a current MLB star. If instead Murphy goes to an auction house, then the house will auction it publicly and take a cut of the sale, most likely a small one since the publicity for the ball will generate income. "We get aggressive too," Marren says. "These names are not private; they're usually in the paper the next day." In other words, Murphy should expect a call if he doesn't call them.
When the seller chooses to put the ball on the market
Nearly all the experts agreed the sooner the better, since the memorabilia market has a short-term memory. "It's all about being en vogue," Steiner says. "That's the risk you take holding onto the baseball. You might miss your opportunity to sell when it's a hot item." All the experts pointed to the case of Walter Kowalczyk, who caught Alex Rodriguez's 500th home run, and who's still debating what to do with it. "The best advice is don't wait too long," Heffner says. "The odds of the value going down are greater."
Whether investors believe A-Rod will eclipse Bonds
As premature as it may sound, Rodriguez's 500th homer on Saturday may have made potential buyers hesitate. Simply put, investors don't want to be labeled the next Todd McFarlane. "[Rodriguez] is a factor in people's minds," Heffner says. "Could this record be broken?" For the serious investor, this might make a huge difference.
Whether the record-breaker is a nice person
Heffner was the lone expert who brought up Bonds' personality as a factor into the ball's worth. "It's one of the most historic balls in baseball history," Heffner says, "It's of great value but would be even greater if it were someone who wasn't perceived as a steroid user, and if he was a nicer person." Heffner felt that those two factors led to the devaluing of the ball. "It should be a million-dollar baseball," he says.
What the values are of the buyer
Both auction house experts agreed that the value of the ball could increase significantly if a bidding war broke out between two companies. The impetus of a company purchasing the ball would most likely be for public relations purposes. Big companies could use it as a promotional tool, for work retreats or other ways of generating interest or buzz for the given company. Or, as both Marren and Heffner point out, the negative value placed on the ball by virtue of Bonds' alleged steroid use could be turned into a marketing tool. "If a company wanted to take advantage of the negative connotation," Marren says, "to make a statement like: We don't agree with steroids. That could bring the value up."
Whether Bonds ever hits another home run again
The experts also were in unison that the most valuable ball is the last one Bonds hits. Barring an injury shortly after he hits 756, the entire league intentionally walking him, or an indictment on federal perjury charges, Bonds will likely hit more than 756. If so, then the final ball he hits out of the park will be the true record, the one which every other player will have to overcome. "I look at  very simply," Steiner says. "It will be of good value. It's the last homer of his career that will be worth the most. What's going to happen next year to him?"
No one can answer that question. Bonds' future is uncertain, and while he has publicly said he wants to play next season, Giants owner Peter Magowan has not exactly endorsed his return.
For McFarlane, the man who knows a bit about valuing milestone baseballs, it's pretty simple.
"I don't think it's the ball," McFarlane says. "The ball is the one where he says, I quit, and the last homer he hit is the ball. Plus, what if he [had hit] 756 and 757 in the same game? Say the guy who caught 756 [was] sitting next to the guy who caught 757. He's not the guy with the best ball anymore."
McFarlane says he'll bid a decent amount for No. 756, but he'll bow out once it gets out of his range. But for the final home run of Bonds' career?
"I'll go all-in on that one," McFarlane says.
Amy K. Nelson is a staff writer for ESPN.com.