Amazon currently has a promotion for buy 3 for price of 2 on select items, including vinyl and some NIN albums are part of this: The Downward Spiral, With Teeth, Not the Actual Events, Add Violence, The Fragile: Deviations 1, Watchmen: Volume 1, Watchmen: Volume 3
I'm not sure if this is just for Prime members!
*10/17 edit - TDS and With Teeth are no longer part of the sale*
*10/19 edit - that's a wrap!*