Brady Hill used his skills for buying and selling baseball cards to purchase his first car and to pay his way through Louisiana State University.

Now that he’s the chief executive of Greensource, one of the country’s largest T-shirt printing companies, Mr. Hill is again devoting time and financial resources to his hobby.

“Seven or eight years ago, I went to see these cards I had in my safe deposit box that I was going to keep forever,” said Mr. Hill, 47. “I said, ‘This is cool.’ Then I looked on eBay and said, ‘Wow, this is legit.’”

Prices have certainly risen for collectible trading cards. Over the past decade, as the Standard & Poor’s 500-stock index has roared back from the 2008 crash, an index of the top 500 baseball cards has done even better — beating it by more than double.