i'd say prob $50 to $75 a day for alcohol... then another $50 a day for things like food, cover charge for clubs (although there are places which are still good that are free - like beer garden at surfers...) and there's always other things that you'll spend money on...
if u are going in the first week to surfers make sure u head down to the beach - always free stuff going on - giving away phones, free food, surfing lessons etc... and they have beach parties at night (under 18's are allowed) which are pretty good... that's what it was like last yr anyway