2000 Volkswagen Passat What rotors to use

Brakes problem
2000 Volkswagen Passat 6 cyl Front Wheel Drive 100000 miles

I'm replacing the rotors on this car, and the price range in aftermarket rotors runs from $20/$30 up to $120 and more. What drives the difference in price? And more importantly, what should I look for in a replacement rotor? Brand? Material? Other?

Thanks.

Wayne Arny