car-functions.php

<?php

add_filter( 'facetwp_filtered_post_ids', 'car_zero_priced_last', 10, 2);
function car_zero_priced_last( $post_ids, $class ) {
	
    if (!isset($class->ajax_params['http_params']['get']['fwp_sort'])) {
      return $post_ids;
    }
    if (isset($class->ajax_params['http_params']['get']['fwp_sort']) && $class->ajax_params['http_params']['get']['fwp_sort'] != 'price_asc') {
      return $post_ids;
    }

    global $wpdb;
    // Lookup zero priced post IDs
    $sql = "
    SELECT post_id
    FROM {$wpdb->prefix}postmeta
    WHERE meta_key = 'price' AND meta_value > '0' AND post_id IN (" . implode( ',', $post_ids ) . ")";
	
   
	  $results = $wpdb->get_col( $sql );
    $diff = array_diff($post_ids, $results);
	
    // default sort, zero priced last
    $post_ids = array_merge($results, $diff );

    return $post_ids;
}