output only if within a combination of two cats

Your query has some odd elements like 'meta_value_num' => '', but it sounds to me like what you want is exactly what category__and does.

$my_query_args = array( 
     'posts_per_page' => 10,
     'meta_key' => 'price',    
     'category__and' => array($catid1,$catid2),   
     'orderby'  => 'meta_value_num', 
     'order' => 'asc'
);

Side note: your price meta key will not order in a way that you think is correct unless the associated values actually are numbers.