If you know anything about baseball cards, you know a Hall of Famer’s rookie card is worth serious money.

For example, the first George Brett baseball card printed in 1975 retails these days for around $60, while the multitude of other pasteboards featuring the Royals’ Hall of Famer aren’t worth much more than a couple of bucks apiece, if that.

Then again, 60 bucks is a whole lot cheaper than two other must-dos for Brettophiles — checking out his plaque at the Baseball Hall of Fame and visiting the stadium where he first donned a professional baseball uniform. Those two shrines are located, respectively, in Cooperstown, N.Y., and Billings, Mont.

While I don’t consider myself a Brettoholic, I’ve been to both. Obviously, Cooperstown is the more impressive site, but Cobb Field in Billings has a charm of its own.

Located a few blocks north of downtown, the home of the Billings Mustangs of the Pioneer League is one of those throwback parks so difficult to find nowadays. Anytime you find a ballyard with a roof over the grandstand, you know you have discovered an anachronism. Some day they all will be gone.

Because the Pioneer League is in the rookie classification, the seats are dirt cheap. You can’t sit in a box, however. The box seats — actually uncomfortable metal folding chairs — all have been sold to season-ticket holders.

Everybody else has to cough up a $5 bill. The fin entitles you to sit anywhere you’d like, whether on bleacher seats or plank seating with a metal backing. The wise fan sits on the third-base side so the setting Montana sun doesn’t fry the back of your neck.

No doubt the Billings baseball facility, also used by the city’s Legion baseball teams, has changed little since 1971 when the Mustangs were a Royals’ farm team and Brett, Kansas City’s second-round draft choice that June, made his professional debut at the tender age of 18, fresh out of El Segundo, Calif., High.

Although a Cincinnati Reds’ farm club now, the folks in Billings haven’t forgotten Brett. His picture is among 10 former Mustangs — most of them future Reds — affixed to the wall of the tunnel under the first-base stands. The only other future Royals’ player pictured is Ruppert Jones, an outfielder whose sole claim to fame is that he was the first member of the Seattle Mariners ever selected for the All-Star Game. That was in 1977 after the M’s snatched him from the Royals in the expansion draft.

Still, no member of the Mustangs ever has made as much of an impact on professional baseball as Brett, who, curiously, did not produce eye-popping numbers at Billings. In 68 games in his rookie pro season, Brett batted .291 with only 18 extra base hits, including five home runs. And he made a ton of errors. Nevertheless, he was the league’s all-star shortstop.

Two summers later, Brett was playing for the Royals — an astonishing leap for a player who had signed a pro baseball contract out of high school.

After watching the Mustangs tangle with the Casper, Wyo., Rockies one night last week, I couldn’t help but wonder if I was watching any future major leaguers. Talented players aren’t difficult to spot, and the best-looking player I saw that night was the Mustangs’ center fielder.

His name is B.J. Szymanski, and he was the Reds’ second-round draft choice out of — believe it or not — Princeton University. A switch-hitter who stands 6-foot-5 and weighs 215 pounds, Szymanski not only looks good in a suit, he can play.

In the Mustangs’ 3-2 victory over Casper, Szymanski hit a solo home run over the right-field fence, doubled to left and threw out a runner at home plate. Also a talented wide receiver in football, Szymanski passed up his senior season at Princeton to sign with the Reds.

Will B.J. Szymanski be the second former Mustangs’ player to make the Hall of Fame? Hmmm.

Or is there only one George Brett?