Like Xeno said, your question has a very broad based answer, specially for a city like Karachi, where you can find classy apartments in bad areas for 10,000 a month, and bad apartments in a classy area for 50,000 a month.
In Karachi, I reckon, for a middle class family, 25,000 rupees a month is a good figure, where you can expect to spend around 10k on rent and utilities, 5k on food and groceries, and then some money for transportation, which again varies, depending on whether you ride a Civic, or a W-11.
that was 10k for an apartment in defence... would that be a bad apartment in a classy area?
Which areas would you recommend?