My favorite “found money” movie is this one:
https://en.wikipedia.org/wiki/Charley_Varrick
Charley Varrick (aka The Last of the Independents and Kill Charley Varrick) is a 1973 crime film directed by Don Siegel and starring Walter Matthau, Andrew Robinson, Joe Don Baker and John Vernon. The film was based on the novel The Looters by John H. Reese.
Charley Varrick is a crop-duster and former stunt pilot. Charley, his wife Nadine, longtime accomplice Al Dutcher, and youngster Harman Sullivan rob a bank in the rural community of Tres Cruces, New Mexico.
When they count the money, it totals $765,118, much more than expected. After a local news broadcast reports that only $2,000 was stolen, Charley says the bank must be involved in a money laundering operation.
Oooo! Another one to look for. Thanks!