I got 2 answers in the comments – thank you both for participating.

El Guapo said $425, and llman – $325. llman, you’re a pessimist!

I probably look naive or something, ’cause after seriously intense calculations, my “handler” looked me straight in the eye and said:

$400 even.
 

Having done my own math, I questioned that number. Also got a little mad, but spoke very calmly.

They have screens with live spot quotes all around, and use Buying and Selling prices, like with the currencies. At the time Buying price in CAD$ was $34.52.*

I showed her my logic on the calculator. Including their commission, my net came to $436, but she couldn’t let me have it and rounded down to $430. If it was a bigger amount, I would’ve questioned it, but ok… whatever.

The answer: $430.

5-12% of silver is lost during smelting so I figure they made about $70-120 on this transaction.

* Selling price was around $38.40.