I'm struggling to find out hoe to remove the default currency set to USD and after wondering in TEC's code, I've found put that the currency is actually stored with in the amount field. However, I didn't manage to find where this happens in the plugin's code.
But the most important think is: why you did something so silly?
The cost field must contain just ... well, the cost!
There's not just USD in the world: so what's the point of putting it as a default and only and mandatory currency?
Now, in my template, I have to use a stupid substr() function to remove this currency and replace it with the one I need EUR.