Did you ever find a solution to this? I was looking to do the same thing.
I dont have anything behind rounded numbers so i added it simple in template file. Matter of appearance, visitor will never know.
<div class="invoice-row-right"><?php the_sub_field('net_price'); ?>.00€</div>
But if you have something like this 59.75 €, it wont work of course.
When you’re outputting the field in your template, use PHP’s number_format. Example:
<?php echo number_format( floatval( get_field('price') ), 2, '.', ',' ); ?>
floatval converts the custom field string into a float, and number_format constrains the number to 2 decimal places, and adds the comma.
On the admin side there doesn’t seem to be an easy way to add a comma to the “Number” field type.
