Ibiza to Formentera passenger ferries. Summer 2010

Last year we flew into Ibiza, into a taxi then caught the ferry to the near
by island of Formentera.
The prices were very high, we got a slight reduction because of our senior
age.
For the return journey we bought the tickets at the hotels reception at a
better price.

Any one done this journey and know how to get the best price particularly
the outward one from Ibiza.

Regards
David