A piece of culture (a song, movie, book) I encountered recently that has to do with money is the first Harry Potter movie–Harry goes to pick up his savings from the bank, but it’s in wizard currency (galleons, sickles, etc).
To write a rhetorical analysis, I would start with figuring out how the monetary system of Harry Potter would translate to real life. I would also look at the real life consequences of the book itself being published. I could do research on the number of book sales and how the sale of Harry Potter books helped contribute to the British and American economies.