Assuming only for one person.
Accomodation: (Single bedroom) $ 500 - 1000
transportation $50 - $100 (depending on where you're going)
Mobile or phone bills $20 - $100 (depending on how much you'll talk on the phone) a cheap cellphone can be bought for as little as $50
electricity, gaz & water bills $100 (if it's not included already)
eating $50 (for groceries or takeout)
entertainment $100 - $200 (dining out, movies, coffee shops..etc)
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So you're looking at $850 to $1500
Note: Maximum estimate reflects a somewhat flamboyant lifestyle. So you'll excuse me if they're a bit exagerrated!
:P