WHY I paid for much duty tax?

I purchased $260 of clothes off of the Metal Mulisha website. I paid $30, ground purolator shipping. When I went to pick up my crap from the post office, they told me I had to pay $130 for duty taxes!! WHAT THE HECK? any reasons why this is what it is? I don't know anything about duty taxes....but I could have bought this stuff from a store instead of paying ridiculous amounts for it online!! Shanks.