What the ‘cheap date index’ shows about global prices

In some cities, even a "cheap date" can burn a hole in your pocket.

According to Deutsche Bank's Cheap Date Index – which measures the cost of a movie-and burger date in 32 global cities in U.S. dollar terms – London is by far the most expensive place for a simple night on the town, while Mumbai is the cheapest.

The index measures the cost of cab rides, McDonald's burgers, soft drinks, two movie tickets, and a couple of beers.

In London, this basket of items would cost $121, compared with just $23 in Mumbai.

"With the cheap date index, what we were trying to work out is a proxy for the cost of living without taking real estate costs directly in there," Sanjeev Sanyal, global strategist at Deutsche Bank told CNBC.

The index was launched in 2012; however, its components have varied slightly in previous years, making it difficult to draw precise historical comparisons.

While it's no surprise that London has topped the ranking, Mumbai's placement at the bottom reflects a curious dynamic.

"India is an interesting case – it's cheap even though it's continued to see high inflation – and that's because the exchange rate is correcting for it," Sanyal said.

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While the rupee has regained some of its losses against the greenback in the recent months, it is almost 12 percent below levels seen two years ago. The currency has been under pressure due to structural issues in the economy including its twin - current account and budget - deficits and elevated inflation.

A notable trend that has emerged is the declining cost of living in Tokyo – a city that has been synonymous with an excessively high cost of living.

Tokyo has topped a few of the traditional cost of living indices in the recent years. However, weakness in the yen - which fell over 20 percent against the dollar last year - has pushed it off the top of some rankings. In the Economist Intelligence Unit's cost of living survey published in March, for example, Singapore topped Tokyo to become the world's most expensive city.

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A "cheap date" in the Japanese capital city costs $100, according to the index – below London, Wellington, Edinburgh, Sydney, Berlin and Paris.

"Everyone has this image of Japan being outrageously expensive, but it's no longer the case," Sanyal said. "Due to a weaker yen and the cumulative impact of years of deflation – there are many cities in the world that are now more expensive than Tokyo."

The index reflects another important trend: China is getting more expensive, said Sanyal.

"China is no longer the very cheap location it used to be, it's slowly converging with world prices," he said.

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A cheap date in Shanghai, for example, costs $61 - compared with $26 in Manila and $36 in Kuala Lumpur.