Shipping costs are calculated by item weight. The best way to understand your shipping costs would be to add all your items to cart, check out and then preview your shipping costs on the payment page. This applies to both domestic and international orders.
The shipping costs you pay at checkout cover us sending the kit to you, and us sending the finished pieces to you. They do not include sending the kits to us. We ask you do this Priority Express with signature as this is the USPS regulation.