For riders starting out, I would recommend a decent second hand bike, where you can get a good bike for £150.
Except you would need to know what you are looking for, in terms of function and erm....state of repair.
You could buy a second hand bike for £100, and by the time you've had all the bits replaced that may need it, end up spending more then if you bought an entry level bike for £200 new.
Anyway I digress....