Hiya, The hair extensions I bought were from a trade/beauty shop called Flo'mans There are loads of the same type all over the place.
The ones I got, you had to buy the clips seperately and sew them on, so make sure they are really secure and the did stay in, as long as I left them alone and didnt fiddle, I was convinced they were going to fling off on the middle of the dancefloor but they never did!
You could try the market but I used human hair ones as I didnt want them to look syntheticky ( is that even a word..no)...I would expect to pay around �30 quid depending on the lenght you buy, though dont go too long as it looks really noticeable....
xx