Good question! You can obtain a shipping estimate from your shopping cart before going through the checkout process. Simply load your shopping cart, click the green cart icon in the menu area, and select "Get Shipping Estimate" on the right, within your cart.
Shipping costs vary by country and the amount of product ordered. Even if you bundle many products in a single order, the shipping cost remains pretty reasonable with a fairly low maximum cost. Try it!
We're currently working on a teleportation device that will allow us to beam the shirts directly to your house at no charge (we're skipping over the whole drone fad), but until our device is complete, we're stuck using the mail just like everyone else.