Ok, First, it matters if you get a lot, or individual cards. Individual cards are a lot more. Lots are cheaper, but the cards are more random. I am guessing you don't want 10 Euros worth of energy cards.
Usually on ebay, you can get a lot of 50 cards for $10 (7.48 Euros)
Or you can get a lot of 20 cards with a guaranteed EX/FA for the same price