I've found that you have to get a really good price on any item from the US to make it worthwhile ordering from there, or an item that's impossible to get here.
With the exchange rate and shipping, you can almost double the cost in US dollars. Shipping is sometimes exorbitant. (Not necessarily Nashbar, but it's something you really have to check.)
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"...perhaps the world needs a little more Canada" - Jean Chretian, 2003.