Does Aeron count as first card for the effect?

There's no card named "Aeron" in the database — I'm assuming you mean Astral Heron. Yes: it counts as your first card. Its trigger checks after it finalizes on the battlefield, so it sees itself as the first card played, and the discount applies to your next card — the second card you play that turn (Rule 419.4.a). It never discounts itself.