Well, the Chinese stores sell them for about 3€ or 4€, it depends from what you want.
Of course that if you go to a big electronic supplier, that they will charge it much more then the chinese. However, look for the safety side of the thing: I rather prefer to pay 8€ for a thing knowing that it's secure and certified, than to buy it on a chinese store.
And trust me, that kind of product it's not trustworthy to be bought on a "low cost" place. At the Hotel where I work, if we didn't hade any safety measures on the rooms electrical boards, I think that probably ate least in the last 2 and a half years (the time that I'm already working in there) the Hotel could be burned to ashes in 4 or 5 times just because of chinese products.
Best Regards
Diogo