How do I Calculate the Total Cost of a USD Purchase?

I'm looking to buy something that costs about $650 USD.

At the current exchange rate that's about $890 CAD.

What surprise fees am I going to see when it gets up here? Better yet, how do I make sure that the site I'm buying it from uses CURRENT AT PAR exchange rates without some other dumb conversion fee?

Also, I'm in Ontario.

Thanks guys