Oracle Text

Any player may cast creature spells with converted mana cost 3 or less without paying their mana cost and as though they had flash.

Card Rulings

10/4/2004 The mana cost of the creatures being cast is still the stated cost on the card, even though you did not pay the cost.
10/4/2004 Aluren checks the actual printed cost on the creature card, and is not affected by things which allow you to cast the spell for less.
10/4/2004 You can’t choose to cast a creature as though it had flash via Aluren and still pay the mana cost. You either cast the creature normally, or via Aluren without paying the mana cost.
10/4/2004 You can’t use Aluren when casting a creature using another alternate means, such as the Morph ability.
8/1/2008 If creature with X in its cost is cast this way, X can only be 0.