It might be cheaper to ship from China to the US than to ship from Chicago to NY, but it is also far slower. I think it's fair to charge less for "as you have space" shipping. http://track-chinapost.com/?p=774

I've had a couple hundred small packages (components for prototypes, tools, etc.) shipped via China Post in the last few years, and only 2 of them arrived in less than 3 weeks. Several didn't arrive at all. I'm not willing to pay as much for that kind of service as I am to send a package from e.g. Chicago to NY with fast and reliable delivery.

The rates are probably unfairly low, but you can't look only at the price. You have to look at price, delivery speed, and reliability at a minimum.