150e each you should be fine but you just have to be sensible to make sure you don't blow it. Depends how much you'll drink it clubs, half board will save you money if you make breakfast. Are you hiring a car, will you eat lunch, how much will you drink at bars during the day etc etc.
To be honest I've never came back from ibiza with any money as you live to your means as it were. but On my second proper Ibiza trip I did come back 2 days later than planned and a grand worse off.
I'm aiming for 150e a day myself this year with 3 club nights planned in a week