Agree about Jury's Inn. ^
Another possibility we use is the Bath Road Premier Inn. This can be really cheap - we are paying £39 for the family for the night in April. £55 is usual and it is comfortable and clean.
If you get off the tube at Hounslow West, there are at least 3 buses from the stop across the road, (222, H98, 81) which will take you along to 'Oxford Avenue' stop. This is right outside the Premier Inn.
To get to T5 next day, catch any bus one stop to Harlington Corner, then get the 423 from there which takes you on a pleasant route past a few NIMBY houses to T5. This journey is free, as it's in the Heathrow zone.
This approach is cheap, especially if you don't mind using the bus. We don't. Of course you could use the taxi or hoppa if you want.