See, that's just the thing -- I don't think we can extrapolate at all, really. We don't know enough about what gil represents or how the economy works to really guess how much such a thing would cost. If you go by in-game costs directly, you'll probably get a very inflated value. If you try to construct a purchasing parity index similar to the quick and dirty "Big Mac Index" -- let's call it the "Potion index" -- and link it to a similar commodity in country of similar economic structure, you'll probably come up with weird values because the costs in game are set for game balance, not economic accuracy. 
That said, if one did want to go down the PPI route, I'd recommend creating either a basket of goods or one specific good -- say, the cost of a cheap meal at the Bismark -- and call it an index value of 1, equivalent to a fast food meal in a related real world country. Then, compute the index multiplier in that other country for something you want to value in gil, then convert back from the index to the cost in gil.
So, for instance, let's say a cheap meal in Limsa costs 10 gil in game. That's index value 1. For the sake of argument, let's say a cheap fast food meal in a coastal fishing city in US runs around $5. A cheap apartment there is $465 per month. That gives it an index value of 465/5 = 93. So, in Limsa, a cheap apartment would be 93 * 10, or 930 gil per month.
Obviously, one can easily poke holes in the above analysis, which is why I don't like it very much.
I'm not really satisfied with this state of affairs either, but I just don't think we have enough information to do anything other than call gil an abstraction of relative wealth for now.
That said, if one did want to go down the PPI route, I'd recommend creating either a basket of goods or one specific good -- say, the cost of a cheap meal at the Bismark -- and call it an index value of 1, equivalent to a fast food meal in a related real world country. Then, compute the index multiplier in that other country for something you want to value in gil, then convert back from the index to the cost in gil.
So, for instance, let's say a cheap meal in Limsa costs 10 gil in game. That's index value 1. For the sake of argument, let's say a cheap fast food meal in a coastal fishing city in US runs around $5. A cheap apartment there is $465 per month. That gives it an index value of 465/5 = 93. So, in Limsa, a cheap apartment would be 93 * 10, or 930 gil per month.
Obviously, one can easily poke holes in the above analysis, which is why I don't like it very much.
I'm not really satisfied with this state of affairs either, but I just don't think we have enough information to do anything other than call gil an abstraction of relative wealth for now.
The Freelance Wizard
Quality RP at low, low prices!
((about me | about L'yhta Mahre | L'yhta's desk | about Mysterium, the Ivory Tower: a heavy RP society of mages))
Quality RP at low, low prices!
((about me | about L'yhta Mahre | L'yhta's desk | about Mysterium, the Ivory Tower: a heavy RP society of mages))
