Dont laugh,
I use rotors bought at my local discount auto parts store. But before i put them on the car I throughly clean them, then give them a couple of heat cycles at work in a self-clean oven. temp's get anywhere from 900 to 1000 deg. oven takes a while to get to temp and a while to cool down. after baking they're pretty much good to go. That's my hand-me-down secret of the day.
P.S. i've gone 2 weekends and an enduro on current set. hawk blues on all corners, and still no cracks. not even the little ones.
brake ducts and shhhhhhh, misters from the washer bottle, attach the washer pump wires to your brakelight sender switch but dont tell anyone shhhhhhhh.
I had the same problem with cracking rotors until I switched to the Mazda Comp duct system that ducts air to the center of the rotor and started buying heat treated rotors from Porterfield (the last set were Brembos). Haven't cracked a rotor since...of course I keep a close eye on them and change them when you start to see too much of the surface "spidering".
I don't remember the price off the top of my head, but i think they were either $56 each or $65 each.....which is what I paid when I ordered "OEM" rotors from the local dealer.