Originally Posted by
Jagboi
As a data point, a black cab from Mayfair to T5 leaving Mayfair at about 2 pm cost me £78. Personally, if I was in the OP's shoes I'd take the tube as it's about 50 min from LHR to Green Park.
So would I. The OP has not said where in Mayfair he / she is heading, but as I said earlier, there are 3 tube stops on the Piccadilly serving Mayfair so the chances are one of them will be a few minutes walk from the destination.
I don't understand this fixation others have with the HEX then a taxi. It will also cost 4-5 times the tube too.