If you go to a shop, and the evods are £5-6, that's not too bad...but ask if they are made by Kanger.
The "copy" evods cost 70p - £1.50 from China. They are mostly **** (poo).
You might get lucky, but normally, what happens is a shop sells you 3 and some replacement heads for £2 each as well. You've then spent £25 on something you could probably buy for a tenner.
There is a Staffordshire chap on here, he knows the shops.