You know you want.
I can’t improve on Pat Kilbane’s explanation at Mythodrome:
A bundle of cash is a powerful emotional trigger. In fact, human brain scans have shown that the idea of money stimulates the same primal pleasure centers as food, sex and cocaine. So what does this tell you? That if you’re going to use prop money in your film or photograph, you must make it look as real as possible for maximum impact. Here is an abridged how-to guide to making a top-notch bundle of prop money.
How to make fake cash: $50,000 Prop Money, Pat Kilbane>>