Data mismatch error when running custom function to update field in Deals module

Data mismatch error when running custom function to update field in Deals module

I keep getting an error message:  Failed to execute function Data type of the argument of the function '754' did not match the required data type of '[BIGINT]' Line Number:XX

I'm trying to covert a currency field value to a text field string that includes a $ symbol, thousands separators and 2 decimal places.   I can't figure out what I'm getting wrong.  

Here is what I have:
Custom Function & Error