You can't find a real world equivalent. Look, for example, to FFVII. We see the villa sold for 300,000 gil, which would seem to suggest relative similarity between the gil and dollar. At least,one can interpret that as such. However, we see that a "Today's Special" meal at the restaurant in Wall Market costs 70 gil, which certainly seems very extravagent given the appearance of the restaurant. These are at least somewhat compatible with real world purchases, yet we see a disparity in exactly what a given amount of gil is able to do. Even if you disagree with my assessments of the costs, it should be clear that there is a disconnect between the monetary value of gil and that of any actual currency.
Using the Equivalency scale DJZen formulated:
1 gil - $.05
the Villa = $15,000
The Meal = $3.50

A very small house can cost 15,000 here in the states, and a meal can be 3.50 or more at the sleaziest McDonalds too. The size of the Villa and its beachside location would, if Costa Del Sol was in USA, be MUCH higher. Around the $250,000 range.