AYou'll be breaking the bank with edible images, sorry.
I'm no where near a pro, just a hobby baker, but I really don't see anyway to get that look without using edible images. Sounds like a case of 'if she wants it, she's gotta pay for it' to me. Why fret over how to make the cake any way other than edible images & drive yourself crazy? I'd do it how I best felt comfortable & if the client doesn't like your quote with the crazy amount of edible images needed then let them make it themselves. Is it even illegal to copy currency, even if it is on an icing sheet & meant to eat?
All I could find was a $5 though. The $100s were only like 2x3", not full bill size.
ADitto to what's said above
I know that over here you can get rice paper that looks like money for not very much cost at all. It's available in most sweetie shops, or there are lots of options on ebay (search rice paper money). Just wrap one sheet round a cylinder of fondant, and there you go!
It's not illegal to copy currency, it just has to be like 75% or 125% the size of actual currency.
I have given her a quote with the added expense of the edible images, just wasn't sure if anyone had some amazing trick to get the same effect. I figure with the 2 tiers that I will probably need 36 bills (cut in 4 for each "roll")