yep, if you get tumbling noise during highway breaking, that's caused by warped rotors for sure.
and yep, rotors costs a LOT..
make sure you get good rotors... they last a long time. bad rotors tend to warp really fast
but then again... changing your own rotors doesn't take too much diy experience
just take wheel off, 2 retaining screws for the brake pads assembly unit, and the rotor will just slide off..