Using Orderby and meta_value_num to order numbers first then strings

Question

I have a list of products, each with a price in a custom field stored as text such as "2.50" or "5.00" and I am displaying them on the page with a custom query that sorts by the price:

    if(!$wp_query) {
        global $wp_query;
    }

    $args = array(
        'meta_key' => 'price',
        'orderby' => 'meta_value_num',
        'order' => 'ASC'
    );

    query_posts( array_merge( $args , $wp_query->query ) );

This works fine for the prices, but some prices are "POA" and I would like to show them last, however the above orders in such a way that "POA" is shown first.

Is there any way to alter this, or a quick hack I could use to sort the array afterwards and put any "POA" prices last?