I thought that if I specified shipping class as “all products in cart” the USPS look-up table app would work correctly. However, it is still giving ridiculously high totals, presumably because it is calculating shipping on each item separately. This is a terrible bug in the woocommerce platform, and I will try to work with them again to fix it. In the meantime, there is a flat-rate shipping option based on average cost of USPS priority mail to your zone, for an average size order. If you only order one item, the calculated price may be less, so I’m including this option.