I'm just back from Heathrow last night. We used Purple Parking Valet parking. I agree it's highway robbery there.
Since we drove up for a 9am flight on a Thursday morning, we didn't want to faff around with shuttles. We missed the parking area and had to exit and go around again, but drop off was easy. Getting back we had to wait about 10 minutes as the cars hadn't arrived. Other than that, it was easy enough there.