Pegasus Airlines offers cheap tickets to Iran. Flights from Spain (Barcelona or Madrid) to Tehran from only 198 EUR round trip.
From September till March 2016. The lowest price is for flights in October.
Barcelona (BCN) – Tehran (IKA) – Barcelona (BCN),
Madrid (MAD) – Tehran (IKA) – Madrid (MAD).
One cabin bag and one piece of checked in baggage per passenger.