I bought an ex race nc30 for £1000,you can get them cheaper if you look around,pain in the bum to work on as space is tight,but cheap to fix if you bend it.
Me and my mates also bought a write off nc30 for about £600,new forks were £100 and a new frame cost us £50,stick on track bodywork and its first race is easter weekend at mallory.
Ask here too
http://www.400greybike.co.uk/Forum/default.asp