Hi Chris. I worked in Ibiza last year and plan to return in either june or aug (depending on job & funds!).
Its best to get out there in june, before the clubs open, to get the best chance of gettin a job. Sayin that, people are always losing/changing jobs or going home..so if you keep your eyes and ears open, you can pick up stuff all season. Go to The Ship which is a British workers pub inthe square at the top of the west end...there's always notices up advertising jobs and apartments available throughought the summer.
On arrival in San An, either head to the Florida Hotel by the Egg roundabout and ask if they have a room for the night. They also rent out the Sol-y-mar apartments across the road which are cheap if available..you'll need ppl to share with u tho. Wips supermarket is outside the Florida..this is workers central...the majority of the guys sittin outside on the blue plastic chairs, drinkin cheap vodka and fanta limon, eatin big bags of cheesy puffs (you can tell how i spent the majority of my summer!!) will be workers in the same boat as u. Go and chat to some ppl, they might even be lookin for ppl to share accom with aswell.
Also, Delilah's bar which is a welsh bar on the main strip on the west end, has accom above it which is extremely cheap. This is charged per night, so its best just to use it while ur lookin for somethin permanent.
The last drop Inn, further up the strip also has rooms above..very plush..but towards the top end of price range.
Dualas (workers bar with apartment block above), Azul apartments (towards sunset strip), and El Moro (near bus stop and harbour) are all frequanted by workers and fairly cheap if u get a load of u in sharing (just dont tell the landlord how many of u are in there!).
Phew..hope that's ok. This is only from my experience last year...others may have better tips for you.
Good luck with everything...maybe i'll see you down Wips!!