Here are some links that mite help in working out where the cheapest place for you is.


STEAM stores.
http://store.steampowered.com/?cc=us     Prices shown in USD
http://store.steampowered.com/?cc=uk     Prices shown in GBP
http://store.steampowered.com/?cc=nz     Prices shown in USD
http://store.steampowered.com/?cc=aus   Prices shown in USD

Conversion sites. (Always Double check converted prices)
http://www.xe.com/   
http://www.oanda.com/currency/converter/