China suppliers seem to get quite a deal. I've gotten components from them shipping included for less than what it would cost simply to mail it here, it's as if the component was free for just paying the postage. How they sent anything internationally for three bucks is suspicious...
I suspect what they do is bundle thousands of postal items in a shipping container, and put it on a container ship. There is so much stuff going to the USA from China, there's probably several ships a day. In China, the labour is so cheap that postal handling charges are extremely low. How they handle it on this end, I have no idea. But it's obviously a well-oiled machine. There must be some money in it for someone! To support my theory, realize that it takes 2-4 weeks for a package to get to North America from China.
I recently bought a proto shield with connectors and a switch from Hong Kong. It was $5 with FREE shipping! It arrived in reasonable time in good condition. I also had to order from one of the big mail order houses a few times. They will only use a courier to ship to Canada from the USA so it was exhorbitant. I only do that when I'm desperate.