try to check get_post_meta($post->ID,'preis');
in your loop
$paged = (get_query_var('paged')) ? get_query_var('paged') : 1;
$args = array(
'post_type' => 'post',
'posts_per_page' => 8,
'paged' => $paged,
'meta_key' => 'price',
'orderby' => 'meta_value_num',
'order' => 'ASC'
);
$wp_query = new WP_Query($args);
if(have_posts())
{
while ( have_posts() ) : the_post();
var_dump(get_post_meta($post->ID,'preis'));
echo get_field('name')
endwhile;
}