Prices vary like any apartment anywhere. Some are in nicer areas, some more modern, some furnished, some not, some have certain bills included... some not. Agencies sometimes charge more than private. Studios will be small in my experience in London.. some tiny..in the heart of the city. My flat now with 2 bedrooms just outside London costs the same as my tiny studio that I once had in Fulham. Some studios mean there is a separate kitchen and some you have a sink near your bed.