I have yet to see any kind of data set that shows BYU fans or Mormons in general are cheaper than anyone else. Why does this opinion continue to be presented as fact? Does someone have evidence showing that it's true?
If anything I think Mormons overspend trying to keep up with each other sometimes.
Also, being wise with savings, spend, and debt structure in your finances is not the same as cheap, but I could see how it would be construed as such.