One quick way to find out shipping is to add a case and the incentive piece to your actual cart, as if you were going to buy them that way without the Battles subscription. Go through the order process as normal, but only up through and including Step 2: Shipping. Make sure you choose the shipping method that your subscription uses (most likely the cheapest available). This will give the shipping and handling rate for the case + incentive.
Don't worry that the total price will probably be different: The case will likely be discounted at the normal $279.99 USD, but the incentive might list at $69.99 USD instead of the $24.99 USD. That's because the system still applies your 30% off a Battles product (case). But this method isn't applying the 75% off the Incentive, instead it's taking just 30% off. None of that matters, though, as the goal here is simply to find out how much shipping and handling will be for the case + incentive. Once you've determined the cost of shipping & handling (and any other applicable overseas costs), just go back to Step 1: Shopping Cart, and remove both the case + incentive.
Whatever you do, don't hit the red Place Your Order button under Step 4: Place Your Order while the case + incentive is still in your cart.
I don't know if the $10.00 USD off shipping that Paizo offers on an order of $100.00 USD or more applies to international customers or not. If it does apply, make sure you subtract the $10.00 USD from the total shipping and handling charge you get from Step 2: Shipping.
Hello goonalan,
Your math is absolutely correct. Since you're okay with that, I'll go ahead and push it to ship. You should receive a shipping confirmation email soon. Thank you!