Being a Canadian, we get the short end of the stick when it comes to importing stuff from the US. When I bought my System76 Lemur laptop, the cost was pretty much as expected.
First, there’s the USD conversion. For me, this went as expected. I used my Amazon (Chase) creditcard, which offers no-margin US conversion rates, so I was charged a conversion rate very close to that on xe.com at the time.
Shipping, for my laptop, cost $88 USD, but I understand that varies based on the cost of the purchase. I didn’t opt for any of the additional warranty or warranty shipping options.
For RAM, the cost of purchasing memory in Canada is much cheaper. (Here, it costs $144 CAD+HST for 16GB, but costs $147 USD to upgrade from 4GB to 16GB).
When the laptop crosses the border, Canadian taxes are added. I estimated these at 13% (Ontario HST) of the CAD-converted cost, and it came out to almost that exactly, including $10+HST UPS brokerage fee. No additional tariffs.