Sid's absolutely right on. Buy 'em at the bars or in the streets next to the bars and work 'em for the best deal. ALWAYS cheaper than at the door. And We Love Sundays flyers can be found on Fridays and Saturdays at many places (on car windows, on the ground, next to phone booths) which offers 25 euro reduction before 10AM and 5 euros off the rest of the day.
NEVER buy them at the door. Always discounted tix to be had beforehand. And some buses (i.e. the Amnesia bus from Ibiza town that runs every 20 minutes from 12 to 3) require that you do in order to get free transport.
By the way, Sid, where did you go? Never saw you once while I was there, mate!