I decided to do some comparing for you all, but then my plans got shot down in flames when I realised very few Duty Free Stores had their pricing available online. For the No5 I've also thrown in an online non-duty price for comparison. If your favourite duty free shop has perfumes (and I used Chanel just because I figure No 5 is quite international, and Chance is becoming popular) I welcome you to put your local price up here.
Anyway this is some price comparison for what I found:
CHANEL - CHANCE - 100ml EDT Spray
Downtown Duty Free - Australia - $113
Duty Free Store - Iceland - 7.590 kr
CHANEL - CHANEL NO. 5 - 50ml EDP Spray
Downtown Duty Free - Australia - AUD$ 106
Duty Free Store - Iceland - 4.390 kr
Strawberrynet.com - USA Online (non-Duty Free) - US$90
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I used the following websites in my mission: