I have lived in London for 8 years and it is indeed very expensive. However there is some very reasonable accommodation to be had, which is also not too far out of the centre. The following web site may give you some inspiration: http://www.studio92.com

For a truly central experience, I can highly recommend either The Delmere Hotel, or Hotel Columbus in Paddington. Very centrally located, only a short walk to Oxford Street and with 3 underground stations on the doorstep. Hyde Park is in your back garden! The following web site gives you all the information you want: http://www.delmerehotels.com

Have a nice trip.

Regards,

Bard Vos Arroyo de la Miel - Costa del Sol (Spain) http://www.apartamentosmundial.com