The bean-counters at Mercer Consulting have deemed Istanbul to be the 15th most expensive city in the world for expats (in a tie with Paris). New York is ranked 10th, London 5th, and San Francisco 34th.

I don't trust their methodology. If I am interpreting their index correctly, they suggest that London is merely 19% more expensive than Istanbul, and 30% more expensive than San Francisco. I assure you, this is not true. London makes New York seem a bargain. My observation suggests that it is at least 30% more expensive than New York, which is in turn 30 or 40% more expensive than San Francisco.* At current exchange rates, Istanbul is far cheaper than any of these cities.

I wouldn't move to London unless I was filthy stinking rich, and even then, I wouldn't.

*Assuming your lifestyle consists of big pimpin, spendin cheese. Y'all know how I roll.