Upvote:2
Offered flight prices are often dependent on your location, for the same flight with the same airline. Typically, if you are in a poorer country, flights are cheaper, and if you are in a richer country, they are more expensive. Check for example Google's flight search (http://matrix.itasoftware.com/), which allows you to pick the 'location' you are booking from.
In addition, the conversion to different currencies is done only once, with a margin, and then used for months, so by the time you book, it could be off a lot. For example, if the airline wants 1000 US$, the booking sites all over the world convert that with a fixed rate - they will have to pay 100 US$, but because you are in country X, they ask N of X's currency, which needs to be enough when they have to pay.