Not and use the Inspector's data formatting to supply the currency format--that will hide any non numeric data in the field unless you click in the field.
There are auto-enter calculations you can use that take a numeric value and format it as currency. You could probably modify one of these to do nothing if there are non-numeric characters in the field.
But I'd look real hard at trying to find a way to put the text in a different field. Entering text and numbers in the same field can really raise a host of complications when you then try to work with the data in this field.