There are a number of hotels nearby, mostly on Bath Road. There is a Hotel
Hoppa shuttle bus available at a return fare of 5 pounds.

You can do a google search with heathrow hotels and you'll find plenty of
websites with discount offers.
As you say, most have cheaper weekend rates.

I'm looking at staying at the Travel Inn which offers a rate of 49.95 per
night at a weekend.
It's quite new, and offers triple glazed windows.
See www.travelinn.co.uk for booking details.

Regards

David Bennetts