Interesting that it's a question I couldn't answer. Probably because I've never had the money.
It may be better to go a little outside of London for best prices - I noticed quite a pleasant-looking shop in St Albans for example (quick, easy and cheap Thameslink journey), although I couldn't tell you what models they have (probably all lower end). There's a big shop in Sevenoaks, although I'm not sure it's any cheaper than in London itself (a guitarist friend who lives in Kent seemed a little disparaging).
1975 Calatayud y Gisbert, Yamaha CG131S.