Or, embed this snippet using GenerateWP WordPress Plugin.

Download

Clone

EDD – Free download (Simple)

$meta_query = array(
	'relation' => 'OR',
	array(
		'key'     => 'edd_price',
		'compare' => 'NOT EXISTS',
	),
	array(
		'key'     => 'edd_price',
		'value'   => 'zero',
	),
);