That's honestly a big part of it; the last time I shipped a t-shirt in a padded envelope to Canada it was nearly $25.00, which was more than the cost of the actual t-shirt. Shipping can be absolutely crippling.
With these new boxes, we calculated up as much as we could and put in some mock addresses to the cost; we should be able to ship most of these for around $5 average, $10 max.