Using the IHG Friends & Family rate I found the Holiday Inn Mayfair to be £169 including tax & VAT. I stayed there in July 2014 w/ family and LOVED the location and proximity to the tube. Take the Piccadilly line from from Heathrow to Green Park station and its less than 1 block walk to the hotel.
Its a fine hotel for one night, and I'd much rather spend a bit more to be in a good location.

http://www.ihg.com/hotels/us/en/glob...0401-_-AM17071