my_unitprice_function for MyMail

if ( function_exists( 'mymail_add_tag' ) ) {

    function my_unitprice_function($option, $fallback, $campaignID = NULL, $subscriberID = NULL){

        $_pf = new WC_Product_Factory();

        //relative products
        if($option < 0){

            $posts = get_posts( array(
                'numberposts' => 1,
                'post_type' => 'product',
                'offset' => $option,
            ) );

            $post_id = (int) $posts[0]->ID;

        //absolute products
        }else{

            $post_id = (int) $option;

        }

        $_product = $_pf->get_product($post_id);
        $price_per_unit = $_product->get_price() / get_post_meta ($post_id, 'sub_title', true );
        return '$'.number_format(round($price_per_unit,2),2);
    }

    mymail_add_tag('unitprice', 'my_unitprice_function');
}