Just throwing ideas out there. But a hq parchment is worth more than a lq bar if the currency as accepted. Or perhaps we arrange it like this, 2 q100 bank notes is 1 iron bar. 4 q50 is 1 iron bar. 8 q25 is 1 iron bar. This is still exploitable though. Also, counterfeit doesn't matter as long as they took the time to make the parchment and write on it. That would just mean lots of inflation.
Another idea, a local map of the ROB standing in the exact center could be currency. Then it is harder to counterfeit, but that doesn't matter, it helps money get into the system. Again, the q is the value. This way work is required, as apposed to just cutting up a hide.