Recently, one buylist posted a buy price of $2.25 for Dictate of Erebos. This is quite a jump, but it should not be surprising. Unless this card gets reprinted, this card could easily be selling for $5 or more in the near future. The card that this is most similar to, Grave Pact, has 4 different printings and is $12!
While Grave Pact only costs 4 mana to cast, 3 of that has to be Black. Dictate of Erebos costs 5 mana, but only 2 needs to be Black. Plus, Dictate of Erebos and the other Dictate enchantments from Journey into Nyx have Flash. This means you can actually cast it on your opponent's turn at a time that would be advantageous to you. Perhaps your opponent plays In Garruk's Wake, which only destroys opponent's creatures. If you cast this in response, that player will have to sacrifice as many creatures as yours were destroyed. It's also just fun to cast this if you had mana open anyway.
Dictate of Erebos has never been, and probably never will be, a Constructed staple. However, this enchantment is so good in Commander that pretty much every deck that has some sort of sacrifice theme - and plays Black - in it will include it. Our recommendation is to hold this Enchantment as long as possible, as the buylist price should only rise with time. If you're looking to buy, you're probably never going to get this cheaper. It's not a card with an obvious place to reprint. Even if it gets reprinted in some supplemental product, as we've seen with Grave Pact, the limited new supply won't hold down its price for long.