eatapeach said:
The original view of 20k to replace is a bit wild, I'm certainly more relaxed about it now having seen that there are options.
Not that wild. It is ~£15k for the disks, another grand or so for the pads and several hundred more for anti-rattle shims, replacement calliper bolts and pad wear sensors. Then OPC labour. And don't forget VAT. The standard answer to the 'how much' question used to be 'about the same as a new Ford Focus', and it is still the same ball park.
Decent steel racing disks with bells are in the £2-3.5k range for a set of 4 though OE Cup disks (which have a somewhat shorter lifespan for track use due to their propensity for thermal stress cracks around their vent holes) from the motorsport catalogue can be obtained for less. Other than steel or refurbishing your PCCBs there is actually a third option too. Surface Transforms make a composite disk that can replace PCCBs - it is a different kind of rotor the the Porsche ceramics and JZM supply them. Not cheap (I seem to recall them being around £8k for the kit including pads but not positive and it may have since changed as that was a couple of years ago), but appreciably less than PCCBs.