I just picked up a playset for $80 on ebay.
I don't think it will go much below that. But I think there is a chance it could go quite a bit higher than that.
Just because there isn't a monoblack aggro deck and/or a monoblack control deck in standard at this precise moment doesn't mean there won't be.
Between this, Go for the Throat, the new Duress, Geth's Verdict, Lashwrithe, that 1/1 lifelinking flyer, and all the vampires, black has all the tools it needs to have a strong format defining monoblack aggro deck akin to Vampires an year ago.
Also, Obliterator makes sui black/the gate a very viable budget deck in legacy, so it will see demand from that format as well.
Monoblack Aggro is a very popular deck among casual players, and Obliterator seems like the type of card that casuals would eat up.

