Antec 300 is a good case sub £50.
Not the best cable management options, but there is a little cubby hole you can hide some away in, and afterall, you can't get the best of everything for under £50.
It has good cooling options though.
Depends what you want really, cooling? looks? cable management?. As I say, you'll probably have to make a compromise somewhere for the price, but knowing what's most important to you will help you decide.