You forgot to add the extra cost of shipping over the border (all shippers, including wholesalers, charge extra to cross that imaginary line), brokerage fees and GST/Customs duties on a BAD day (you just can't argue with a Customs Officer...believe me).

On top of all that, you get the dubious privilege of buying large minimum amounts of items, in advance of anyone actually ordering, at the exchange rate (and credit card surcharges including the new-ish exchange surcharge per transaction) at whatever the exchange rate is at that time. I can assure you it hasn't been this good for very long, and this good rate only applies to goods purchased, like, today!

Then there's (other) overhead costs. Snort!