Today is April 18th, wasn't it?
https://en.wikipedia.org/wiki/Action_Comics_1
Action Comics #1 came out on April 18, 1938. In 1938, it cost only 10 cents which is equivalent to $2 dollars in 2019.
On August 24, 2014, a copy graded 9.0 by CGC was sold on eBay for $3,207,852 it is the only comic book to have sold for more than $3 million for a single original copy.
Happy birthday, Superman