So at first lets look at todays coins... they are useless... nobody uses them... they are garbage...
The main point is that they have no valuse... even if you could melt them to nuggets... still.. they will cost same as material, wich is ineffective.
Idea can be if somebody could make unique coins. Also will be great to have something like Village-City difference.. like you need 2000000 auth to upgrade your village to city. And get coinpress as autority object. Now there are coins unique to city, with name of it stamped on coin...
So now when we will take 1 silver coin and make its value by 1 bar of silver, wich is guaranteed by city, and stored in vault, we can produce money inside city with real price and useful in use... Barter stands is a big mistake... they limit players to a few of products... with money they could buy anything they want.
To make lesser prices we will take 1 silver coin and make it cost 100 copper... same unique so nobody could make the same... but the same guarantee - 1 bar of silver per 100 copper coins.
Now with different citys we have exchange rate for money, and economics is working now...