Your post really got me thinking! After replying earlier, I looked online for more information about classroom economies. I found fake money that looks like real money and can be printed off and copied for classroom use. The website for that is www.MoneyInstructor.com
I also found this website
This one is from the National Council on Economic Education. There is a book on this one that has a bunch of lesson plans, templates, ideas, etc. that are appropriate for elementary school. It also has a sample that you can look at. It looks really interesting, and I think I'm going to purchase the book. Hope this helps!