If you need to keep the purse strings tight I'd suggest staying at the Catalina behind Savannah on Sunset strip. Its cheap and clean,nice and quiet (in Sept, dunno about high season) and and ideally located for watching sunset.
From there its a 2 min walk to 1.6 euro bus ride to Ibiza town, pdb and the decent clubs you're after.
Strange advice from a man who works on a theory that if any anything makes your holiday 0.00001% better, once you're there, then bugger the cost and just do it. (Could make some sort of ad slogan out of that.....erm, hang on a minute.....)