Ohoy.

I was browsing the net elsewhere and saw people buying Battle Chests for 5 eur from Battle.net. However the links does not work for everyone, but if they work on you, it doesn't matter if you're EU or US.

I replaced http's with hxxp's so you can see these really are battle.net-links, and not phising ones.

hxxp://enus.nydus.battle.net/WOW/enUS/client/upgrade-offer/PROMO1?accountRegion=US&accountName=
hxxp://battle.net/account/management/upgrade-wow.html?promo=classicFS5dol

The thing is, these links contain some promo codes, and they lead to Battle.net login, and should allow to make cheaper purchases.

Here's the picture for proof from another site
hxxp://image.noelshack.com/fichiers/2012/35/1346423706-sans-titre-1.jpg

I personally did not try this, but both links seems to be valid what I can tell from the comments.