My experiences (buying bicycle stuff) has always been that shipping from the US is really expensive with a high starting rate. So it has to be either a ridiculously great bargain or unobtainable elsewhere to entertain the idea. The UK though was always the other extreme. Somewhat comparable to local costs and often (sadly) faster than trying to buy retail. The rest of Europe somewhere in between.
Similar experience buying Lego (for my kids of course
)
The local post systems always seem much cheaper than anyone pitching themselves as an international logistics type. I suspect the latter come out well on top for ease of use of the seller though.