On average I'll spend in the vicinity of AUD $150 - $250 on a night of partying, including cabs and what not (not just "direct" partying expenses ie. alcohol or what have you)..
but what i find is that there isn't a positive correlation between the amount you spend and the quality of the night out.. often I find that if I'm having a shitty time I'll start blowing lots and lots of money to get me and the people i'm with fucked up quickly so we don't realise how shit of a time we are actually having. This usually doesn't work anyway.
But when you are with good company and at a good venue, I don't really feel the need to start spending copious amounts of money to get trashed, I can just enjoy the moment.