Custom field totals

Get all of the post ids from the specific post type, loop through them and simply add the custom fields together and display the sum below the post type title on edit.php (Notice the add_filter first parameter, you need to change the products part to your post type name)

add_filter('views_edit-products','products_price_sum');
function products_price_sum($views) {

    $args = array(
        'post_type' => 'products',
        'posts_per_page' => -1,
        'post_status' => 'any',
        'fields' => 'ids'
    );
    $postslist = get_posts( $args );
    $sum_total = 0;

    foreach ($postslist as $post) {
        $price = get_post_meta( $post, 'price', true );
        $sum_total = $sum_total+$price;
    }

    //This is the sum of the price field
    $views['price_sum'] = '<strong>Price Sum:</strong> '.$sum_total;

    return $views;

}