Unless you can Priceline it...

I've taken to staying at the Etap Hotel Hounslow recently - both for LHR departures, and for early o'clock meetings at a nearby hospital. It's a 5 minute walk from Hounslow Central (so about as convenient as a Bath Road hotel for T5), and a 7 minute walk from Hounslow railway station.

It's not a pretty area, but the hotel is solid, spotless and quiet, and costs £39.