Recently came across this publication from Tripadvisor back in June highlighting results from the TripIndex Cities Survey results suggesting some of the most expensive (and cheapest) cities in the world to visit. Results are based a traveling couple (US$). Interesting but somewhat unsurprising results.
Most Expensive are mostly Western European cities. The Cheapest being Asian and Eastern European cities, with quite a few Asian cities missing from the list (as usual).
Here is the survey findings for those interested.