U.S.$

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I favour buying from a Canadian store when the item is available within 10% to 15% of the cost.

One barrier to buying from the U.S. is the cost of customs brokerage plus shipping, especially when you are buying a single item like one light bulb.

It might make sense to arrange a group order of drygoods on a regular schedule, say every 3 months, from the U.S., if anyone is interested.