And is there another measuring stick that would give us the simultaneous jab against globalization and corporate imperialism?
If insulin became expensive during the war, that was only because things became more expensive in general, right? That's what the index should capture: "you need 3x in dollar terms to buy the same stuff in Libya."
Guiness for example is going to cost a lot to ship, or local beer could be very low quality in order to keep the price affordable.
You need something perishable, and of low enough cost that importing is unlikley.
Bread would be a good option but has the issue that it's not as common in Japan as France, it also varies wildley where as a big mac is generally consistent.
So, using something like the potato would eliminate that sort of "bias" to the product, as no one party controls the potato, and thus couldn't artificially set the price higher at a whim. If the price of the potato rose, it would be because the whole market reacted to some changes to transportation or production costs, not because management has decided that they want to build their brand as being expensive and exclusive (which we know happens with a lot of brand products).
2) What if potatoes become hip?
3) If you want auditable PPP conversion rates: http://data.worldbank.org/indicator/PA.NUS.PPP
What is a 'potato'?