It’s smart to have a real badge before ordering one, but as someone who owns real Stone Island (Two jackets, and two sweaters), you will never discover a rep near the standard of the actual thing. It’s something Stone Island prides itself on: How well made their clothing is. Know that going into buying a rep, you will never get near the authentic quality.
You’ve better luck buying something second hand from ebay. I’ve seen jackets and sweaters on that site for the $150-$300 range, and i assure you, it is worth it.