You can always tell an original McQueen piece. And this is definitely an iconic McQueen. (As much as I love Sarah, she just doesn't bring the crazy.)
How much I would pay would depend on if it fits me, and what it looks like on. Also, if it is in wearable condition, and if I could create an occasion to wear it.
If it fits and looks amazing - $300 to $700. If I have an "status" place (a place where people actually care what I am wearing) to wear it - and it fits and looks amazing - $500 to $1000.
If it is badly worn, too tiny, over altered... between $100-200.