Because everyone that has one raves on about them, I now know why.
$1,400 or so. I got mine from the UK but you can get them locally aswell.
You don't know it's there until you put your foot down around a corner. No clunking, banging, chirping, just balls out grip when you want it. The stock diffs suck and it's not until you start playing around with them you realise.