Cheap Paper Currency With Good Security Features

I'm trying to develop a hard-to-copy anti-tamper label, and another forum
poster had the rather clever suggestion that you could cut out the serial
number from any major currency that has high security features, and you
would end up with a very difficult to replicate serialized label. The
downside of course is that you have to destroy the bill and you incur that
cost for each label. Rather than waste $1 per label, I'm hoping to find
some international currency where each bill is some nominal amount, and the
serial numbers incorporate high security features (bands, microprint,
coloration changes, etc). Can anyone suggest such a currency, preferably
one that can be changed for dollars at any major U.S. bank?

--
Will