That's a good price but rear OEM rotor on that car are even higher quality (compared to Front vs Rear) then any after market you could buy.
They serve a dual purpose as the inside of the rotor is used for the handbrake shoes. My Lexus vehicles use the same rotor as your mother's 2015 Toyota Camry and they were all perfect when I replaced just the rear pads.
55k miles on the car and the rear rotors are gone on that vehicle? doesn't sound right to me, the fronts on the other hand make sense.
I would have just gotten your old OEM rear rotors can, they can easily be turned.