Or maybe have the "stack of coin" be for accumulating the same kind of money badge.

So if you've earned 10$ once, you have a 10$ coin in your badge page, with a progress counter till the next "accumulation badge", which is basicly a badge representing when you've had X badges of a specific type.

Ex: Once you have 3 unique 10$ badges, on your badge page you'll see a stack of 3 bronze coins.

Just shooting ideas off here :)