Travelodge have very cheap rooms if you book in advance, I stayed in the Croydon central one for £26 a night, and that was only booked a couple of weeks in advance. (that one has a good rail link to london and some nice trams, but isn't in a particularly good area)

edit: Of course cost probably isn't too much of an issue with most empeggers, as long as we aren't talking Ritz prices