BMW two piece rotors are definitely more expensive, LoL. I came from Mazda side and they have Willwood kits for cheap. Granted, smaller rotors, but still cheap even at RX-8 sizes.
$1699 for 355mm (14") front two piece rotors with six pot forged and billet calipers.
https://www.good-win-racing.com/Mazd...ml?id=8E96FyCE
For race use, you definitely change them often. Road use will see a lot less change for rotors, based on the pad material.