Multi-level currency is an economic system where each currency level is represented by another item class which requires multiple of previous class to purchase.
The idea is to scale item prices by area, making it unfeasible to buy high-level items by low-level characters and create a steep economic progression for each area.
This also avoids the problem of displaying huge numbers for item prices(e.g. Infinity Sword +1 costs 439432953593593 Gold)
Example with x1000 multiplier:
1000 bronze coins buy 1 silver coin
1000 silver coins buy 1 gold coin
1000 gold coins buy 1 platinum coin
1000 platinum coins buy 1 ruby stone,etc (theme can continue with gems)