Hotels I've used at Heathrow:
Premier Inn T4 - Connected to T4 via walkway, then bus / tube or train (with connection) to T5.
Travelodge T5 - Close to T5 but I'm not sure if you can walk, about 10 minutes if so. Otherwise Hoppa only unfortunately.
Travelodge Central - On Bath Rd so plenty of busses but outside the free zone. Cheap and average.
Mercure - Walkable to Hayes and Harlington in about 15 minutes, but then TFL Rail so probably not worth it for the time you have.
Crowne Plaza - Hoppa or paid normal bus (5 mins walk up the road), every 15 minutes, to Central Bus Station.
Travelodge Feltham - Paid bus to T5.

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