In terms of the UK, other cheaper cities in the North have been internationally renowned for being creative centres, most notable Liverpool particuarly in the 1960's and Manchester most notable in the 80s'/90's. Whilst Hull has just been awarded City of Culture status.
In terms of London, it covers such a vast geographic area that there will always be some cheaper areas for struggling artists away from central areas, whether it be parts of the East End or indeed South London.