Bristol and Durham are probably about equal for academic performance - The Guardian puts Durham at 4th in UK for History, and Bristol 19th. However, 19th in UK is still a great academic standard.
As someone who has lived in the southwest for almost all my life (except when I lived in Germany for 3yrs and then Sussex for my first degree), the south west is *insane* for cost of living. Just searching for rooms available on sturents for Bristol returns some mind boggling prices (£300-£400 a week!), with even properties shared between multiple people being so expensive. It's less intense than London but when you look at some of these properties - not by a lot! Even in the scummier areas of the south west it's still super expensive - I've been working in the NHS in the south west in a pretty run down area and cannot afford to live on my own, and would struggle even with a partner to live with, even if we lived in a rough part of my town. The same cannot be said about Durham, where I am going for my masters and firmly intend to stay there after graduating because the COL is so draining down here.
Don't get me wrong, Bristol is a nice place and its cultural and vibrant (personally I liken it to a slightly smaller Newcastle) and I did consider doing my MA at Bristol and commuting in (I live 1-1.5hr away) but I ended up going with Durham because I liked their course better and living costs were a big factor for me, my rent is bills inclusive and just under £150pw.