I'm assuming here that this is a number field. When you click on the block that is displaying this field, there should be a format option. See Screenshot
Using the format option you can then add your currency symbol to the field.
Unfortunately the only way to do this is to use a custom shortcode to parse the values and convert it to currency. This can't be done using the single field block.
You will need to retrieve the value manually and then wrap it with the custom shortcode to convert the value.