sort – Sorting problem price

I have a sorting problem when I do a search the titles are also taken into account whereas I would only like to manage it by price. Thank you.

 $args  = array( 
            'post_type'           => array('product', 'product_variation'),
            'post_status'         => 'publish',
            'posts_per_page' => get_option('posts_per_page'),
            'paged'          => $paged,
            'tax_query'      => $tax_query,
            'orderby'       =>  (isset($_GET("orderby"))?$_GET("orderby"):'meta_value_num'),
            'order'         => (isset($_GET("order"))?$_GET("order"):'ASC'),

 if ($orderby == 'price') {

    $args('orderby') = 'meta_value_num';
    $args('meta_key') = '_price';
    $args('order') = 'asc';

  } elseif ($orderby == 'price-desc'){
    $args('orderby') = 'meta_value_num';
    $args('meta_key') = '_price';
    $args('order') = 'desc';   } 


 $content .='<select class="dropdown-class" name="sort-posts" id="sortbox" onchange="document.location.href=location.href+this.options(this.selectedIndex).value;"><option enabled>Trier par</option>';
 $content .='<option value="?orderby=price&order=asc">Trier par tarif croissant</option>';
 $content .='<option value="?orderby=price&order=desc">Trier par tarif décroissant</option>';
 $content .='</select>';