I buy a weft of really good quality hair and then cut and sew them myself, it works out cheaper and a better fit, plus you can get some exceptional hair this way. I buy Remy (this means the hair folicles are all facing the same way direction, this is important as it reduces tangles) The hair industry isnt regulated so its important to find a reputable supplier, words like virgin, european and luxury usually don't mean very much and in cheaper set the hair can even have been swept up off the floor and then processed and made into extensions! Proper aftercare is really key too, you have to learn how to brush them properly, how to keep them hydrated and try not to wash them too much.
I spend £100-£120 on my Wefts which will give me a full double-wefted set of clip in extensions and I wear them maybe 5 days out of 7. They last me over 6 months, I still have a couple of months wear in my current set and I got them in May.