I was cleaning off some bookshelves this afternoon and I came across a copy of The Wealth of Nations that I borrowed from a local library my senior year as an undergraduate (and never returned, but that's not part of the story)--in 1991. Sticking out of the book was a ticket to an Orioles/A's major league game in Baltimore at old Memorial Stadium (ticket is pictured below):
I know it's difficult to read, but the price of an upper reserve ticket in 1991 was $3.75. That's $6.63 in today's dollars.
An upper reserve ticket to tonight's Orioles/Red Sox game at Camden Yards would run you between $15 and $30.