I'll add a +1 vote for the new(ish) Holiday Inn London Heathrow Bath Road. I've stayed several times now, and it's usually a reasonable £80-ish a night. The adjacent (and connected) Staybridge Suites is also a nice option, if you want a bit more space to decompress. The Hotel Hoppa and local busses are best for getting to those two. For very late arrivals and early departures, I'm about to try out the Crowne Plaza in T4 as that's better connected (by the Piccadilly Line) for silly hours of the day (i.e. when the Hotel Hoppa stops running). Can't say much about this one as I've not stayed there yet, but it's a relatively new hotel so should be well-appointed.
Beyond those two IHG options, my next option for easy-to-reach hotel is the Hilton Garden Inn T2 - again, just one stop away on the Piccadilly Line.