I have found an awesome site and the wigs look and feel amazing. Google wonderland wigs. I've a medium bob in red, brown and blond and they feel soft and real, fit easily and look genuine! The red one is in my profile - I'm doing a fetish 'tongue-in-cheek' picture in it. Under £20 and can't recommend their wigs enough. I've seen girls (at the tv particularly) with incredibly expensive wigs that haven't been half as good. Seriously - get a wonderland wig (and no - I don't get commission) lol - just genuinely amazed!
The only thing about the cheaper wigs is that they tend to shine a lot in certain lights especially when they brand new, a lot of photographers will already know this . I not trying to put you off at all just so you know it can happen, proper wigs are not as bad, but then £100 for one look is a lot to pay. The best manufacture of wigs in the cheaper price range is Lacey Costume Wigs ( New York) they hard to find in the UK Ebay good for them. Most if not all the cheaper wigs are made in china and imported by one or two wholesalers check around for price as the same wig can retail at very different prices just becuse they are branded differently.