If you’re a fan of Texas A&M quarterback Johnny Manziel — or just see him as a good investment opportunity — you can find everything you need on eBay. It offers hundreds of items signed by the first freshman ever to win the Heisman Trophy: photos, jerseys, helmets, footballs.

As a rule, they aren’t cheap. The asking price on one of the cheaper items, a photo, is $67; for a helmet co-signed by the Aggies’ only other Heisman winner, you may pay nearly $3,000. What the owners of the souvenirs have in common is that they are free to make money off them. But Johnny Football is not.

He’s under investigation by the National Collegiate Athletic Association following reports that he accepted $7,500 to sign 300 helmets in January. That sounds like a lot of money until you consider that Texas A&M reaped $37 million in free publicity from him last season, which enabled the school to undertake a lavish $450 million stadium renovation. The 11-2 record Manziel helped the Aggies achieve also earned his coach a raise, from $2 million a year to $3.1 million.

The NCAA has strict rules to prevent students from reaping any financial rewards for their athletic exploits. They can get free tuition, room and board, but that’s about it. Some universities have proposed granting a stipend of $2,000 a year to cover living expenses, to no avail.

If Manziel is found guilty of accepting payment, he could be suspended for multiple games — or the entire season. In 2011, five Ohio State football players, including quarterback Terrelle Pryor, were barred from five games for remunerative activities involving far less money.

These policies date back to an era when college sports were a student activity, not an enormous business powered by wall-to-wall TV exposure. The rules made a lot more sense then.

Regardless of what the NCAA finds, the controversy exposes the gross disparities between the riches the top players generate for others and the returns they get. True, they receive a free college education, but they are required to spend so much time on their sports that they can’t give nearly as much energy to their studies as they should, and many of them never graduate. Players from poor backgrounds may literally go hungry for lack of funds.

Manziel is not one of those. And he clearly benefits from his association with a major college football program that affords him the chance to showcase his talents for NFL teams that may employ him in the future. But there is still something cockeyed about a system that punishes him for making money off of honest work that will inevitably generate income for someone.

A nonfan might wonder: If all Manziel wants to do is play football and make money, why doesn’t he just forgo the college game and head straight for pro ball? There’s a good reason: Under an NFL rule that confers a great benefit on the NCAA, he’s not eligible to play for an NFL team until three years after leaving high school, which means he’s stuck until 2014.

Many of the NCAA’s critics would prefer that big-time programs dispense with the pretense that these kids are students first and simply pay them to suit up for Gridiron U. Or these educational institutions could stop fielding varsity teams entirely, focusing on academics instead.

But the NCAA can improve things without taking such radical steps. It could allow star players to accept fees for autographs, endorsements or appearances, with the money going into trust funds to be tapped after they’ve used up their eligibility. The athletes could even be required to share the proceeds with their schools or their conferences.

Maybe this episode will finally force the NCAA and its member schools to give athletes a share of all the money they generate. In that case, Johnny Football may earn a new nickname: Johnny Paycheck.