My use case is for printing client proposals and estimates. Since Coda has limited currency options and custom values are not allowed, this is my workaround for using my local currency.
Install the Find & Replace Chrome Extension
Format your column as a currency with the $ Symbol.
Use the find & replace tool to change the currency to what you need.
Note: If you refresh the page or update the table this will revert to the $ symbol. But it is useful if you need a custom currency symbol for printing only.