Fix it, don't replace it.
You don't know how your rotor bent. It could of been the brutally bouncy shuttle ride up the side of a mountain, or maybe it was that twenty-yard cartwheel your bike enjoyed into the forest. What ever the case, accurately straighten it with the Park Tool DT-3 Rotor Truing Gauge.
Note: The DT-3 is designed to be used while wheel is mounted in a Park Tool TS-2.2 or TS-2 Professional Wheel Truing Stand.