I think the buses in London are relatively cheap. It's the congestion that's the problem and you don't get anywhere fast. Especially if you're having to pass through the centre. It takes half an hour to get through Oxford street alone. I mostly use the underground, for which I do not buy a weekly/monthly pass, as I never know how much I'll travel any given week. Single fares don't come cheap. Over-crowding is also rather unpleasant. On the good-side, most trains are new, and they even play classical music in some of the stations.
I'm seriously thinking about getting a bicycle! I just don't relish the thought of getting hot and sweaty and battling double-deckers. Not that I don't get hot and sweaty on the tube in any case. Transport gives me a headache. I wish I had a horse,on which to clip clop through the streets.