at heathrow they have the "hotel hoppa" which is a fee-based hotel shuttle--seems a bit strange. I recall the Hotel Ibis at LHR was the cheapest in the area. I stayed at a Sheraton at LHR for appx 70 GBP weekend rate/on sale for one night in the fall--perfectly adequate. (I think the Ibis was either 49 or 54 GBP anytime, but seemed quite a bit more rudimentary). Beware that LHR is a ghost town (at least the terminal where the Concorde arrives) at 1030pm.