Tracy's always got good ideas:
In our house we have one of those electronic toy cash registers. I have to say they come with the flimsiest paper money ever (in addition to the fact that I have a 2-yr old that likes to tear paper). I found with my particular brand that the little drawer is wide enough to accommodate a credit card. So, I printed my own money on the computer (also put family faces on the bills to make it more fun and personal) and taped the newly printed money on all those used-up plastic gift cards. I used book tape, as it was wide enough and strong enough to withstand my 2-yr old's chewing. They really enjoy the pictures and can also use them as pretend credit cards.
We also saved a few old gift cards that have character pictures on them (ie Princesses, Cars, etc) and just written a dollar amount on them. In the past, I've also printed my own Monopoly money. Now I'm looking for ideas for all those little plastic coins that seem to disappear!
Printing your own Monopoly money? LOVE IT. Replacement coin ideas: bottlecaps (metal from soda and beer bottles, or plastic from juice and milk cartons), buttons, or homemade coins stamped out of Sculpey? Wrapped in foil? Other ideas, Parenthackers?