I buy loads of stuff on Ebay, and a lot of it comes from China/Hong Kong/Korea, and it usually comes with free postage, I have never been charged duty on any of it. On the other hand, the two items I have bought from the USA have had relatively high postal costs, and I have had to pick up both items from the post office, and pay duty.
If you want a comparison of postal charges, look on Ebay at items delivered from the USA (postage is as high as a third of the purchase cost), and a similar item from Honk Kong or Europe, where post is frequently free - as is duty, thpough I don't know the explanation for that.
I have just received a motor to turn the turntable in my microwave oven. It came from Korea, post free, it took about 10-12 days, and the total cost - £2.40! ($3.43 at today's exchange rate)