Well on a sliding scale, if APs are £1000, Willwoods will be about £600 and Hi-Spec will be about £0.50.
A mate of mine bought some Hi-Spec front brakes and was ready for driving down there and throwing them through their windows.
I have AP 6600 calipers on my S1 and they have been seriously spanked. No problems at all and the car stops like fook. I am changing them for something different though but not because they don't work, but I need a different shape caliper for one set of wheels I have. They will be replaced by another set of AP calipers.
I have not found the limit of the current set up as fitted to the car because I hold back from braking as long as I feel safe, then stand on them to find I have stopped far too quickly and have to roll up to the roundabout or other such junction.