Shipping cost is not the only problem for you, sometimes the products won't get approved by customs if its send by someone personal on particular country so you need to analyse the receiving country's laws as well before making an estimation because he might say that he didn't receive anything so asking for payback from escrow. If everything clear on the receiver's country then you could ask for $50 for shipment in total and return back if there is any left amount on that $50.