In 1952, McAuliffe of Boston was the official supplier of caps to Major League Baseball team.
A short item in The Sporting News quoted the cap-maker's spokesman, Tim McAuliffe, as saying the Chicago White Sox had the most expensive caps among the current teams.
White Sox' caps of that era were black with a white interlocking SOX monogram on a red background. These cost the team $6 apiece, according to McAuliffe; other teams' cap were $4 each.
Adjusted for inflation, a $6 cap in 1952 would be about $49 today. I see on New Era's website that an on-field White Sox cap retails for $35; with tax and shipping, that probably adds up to most of $49.
Back in '52, McAuliffe said that the New York Giants and Brooklyn Dodgers spent about $600 a year on caps.
McAuliffe also revealed that Dodgers' infielder Billy Cox wore the smallest cap in the majors, a size 6-1/2. He said Dick Kryhoski of the Browns wore the largest cap, but didn't reveal the actual size.