Field editor output value formatted as currency (when using auto output, shortcode, or widget)

functions.php

<?php
// ^ the <?php above should only be in your functions.php file ONCE, at the top

// The filter is field_editor_output_as_value_METAKEY
// where you need to replace METAKEY with the actual meta key you want to filter the output for
// .... as you can see below you can also add multiple filters using the same function.
add_filter( 'field_editor_output_as_value_METAKEY', 'my_custom_format_value_as_currency' );
// Just uncomment the code below to use same handling for a different meta key
//add_filter( 'field_editor_output_as_value_ANOTHERMETAKEY', 'my_custom_format_value_as_currency' );

/**
 * General function to output HTML for custom fields
 *
 * @author             Myles McNamara
 * @url                https://plugins.smyl.es
 *
 * @param    $value    The value before it is output on the listing
 */
function my_custom_format_value_as_currency( $value ){
	if( empty( $value ) ) return $value;
	// We have to set the locale so PHP knows how to format the value
	// http://php.net/manual/en/function.setlocale.php
	// this tells PHP to use $ and format based on english US
	
	$fmt = numfmt_create( 'en_US', NumberFormatter::CURRENCY );
	// You MAY need to use en_US.UTF-8 if the above is not working
	
	// Make sure to remove currency symbol and any commas
	$value = str_replace( array( '$', ',' ), '', $value );
	// Make sure to convert to useable value (in case using formatting on frontend)
	$value = floatval( $value );
	
	// Currency code from https://en.wikipedia.org/wiki/ISO_4217
	return numfmt_format_currency($fmt, $value, "USD");
}

Combine this with this code to create a currency field from standard text field:
https://gist.github.com/tripflex/d49cc84fc05c77cf9662

https://www.php.net/manual/en/numberformatter.formatcurrency.php
https://en.wikipedia.org/wiki/ISO_4217