Corey Shanus remembers when he bought his first pack of Topps trading cards in the fall of 1963. Like many elementary schoolboys back then, baseball was his favorite sport and cards were the cheapest and easiest way to indulge in his love of the game and its players.

It was also the steppingstone to a lifelong affair with sports memorabilia. What started with trading cards has turned into bats, baseballs, photographs and even historical documents dating back as far as the advent of the game in the early 19th century. Thanks to his successful career in real estate, Mr. Shanus has been able to spend tens of thousands of dollars on one-of-a-kind items, including perhaps the most famous trading card of them all, the 1909 Honus Wagner T206 trading card, which he bought in 1984 for $25,500.

“It’s not what you collect, but the pleasure you get out of it,” said Mr. Shanus, who grew up a Yankees fan and lives in Westchester County, north of New York City. “I loved baseball and I love collecting and it does something to me.”