It is around 20-30 for duty/taxes, but they will still sting you for the "brokerage" fee.
I had $15.00 in playing cards from Ebay sent UPS. I had no idea the seller was going to ship UPS, and got stung with a $40 brokerage fee from them
Got an awesome deal on some subs, $50 for a fully enclosed set! FedEx stung me for another $30 in brokerage.
But you are correct, sometimes (albeit rarely) they'll let stuff through with no brokerage fees or taxes.