how to get the price of items which are added from Add Item(s) button

Hello,

I have some product which does not have price. Lets say Product ABC.

When a customer buys Product ABC, we add that to order manually from Add Item(s) button on Order detail page. We add the price from here only.

But, the invoice is still showing Rs. 0.00 as the price even though we add the pricing manually. Below is the code which fetch the price on invoice.

<?php echo number_format( round( $product->get_price(), 2 ) , 2 , '.' , ',' ); ?>

What will be the correct way to fetch the price for such products mentioned above?

Also, how can we know which products are added manually on the orders list?