Wanted: Small complete bike for a woman ~ £150

Hi all.
My sister needs a bike - she's got about £150 to spend.

Requirements:

• small frame about 49cm (steel or aluminium)
  
• preferably a complete bike but if you've got a cheap f+f lying around I might be interested.
  
• fixed, singlespeed or geared, not fussed.
  
  

It doesn't have to be anything too fancy, just something functional.
Cheers.