Well, I am from Canada, the game on Steam here is 79.99$ which is about 89$ after taxes, but I have seen it on Instant Gaming at about 63$ so yes, you may get the game for cheaper if you look well before buying.

For myself I already bought the game and I didn't know GoG at the time (I bought the game more than a year ago xD First pre-ordered game) so I simply bought it on Steam at full price