Welcome to the community, Mark! Unfortunately Airtable’s currency formatting options are very limited. Not only is there no way to change the default formatting, but that lone formatting choice applies to all values in the same field.
The only way around this would be to craft your own custom formatting formula, but that would put the resulting formatted currency in a new field, not the same field where it was entered. Something to keep in mind. In the meantime, perhaps check to see if there’s a request in the Product Suggestions category for more currency formatting options, and add your input there. If not, feel free to start a new thread.