Wow 35k on a set of rotors!
Did these guys actually measure the disk thickness? base it on a visual check? I think 35k is a reasonable service life for front brake pads but not for rotors. You said the brake warning light came on, that tells me that its time for the pads to be replaced for sure.
Aftermarket OEM rotors are available at most auto parts store, so I’m not sure what the guys at the garage were feeding you. Also factory rotors can be had for around $85.00-$90 (about $20-$25 more than aftermarket OEM), just need to look around.
Most dealerships will not replace pads/rotors with that much mileage because they are considered “wear items”, however if you take the car back to the dealer where you bought the car from, they will work with you most of the time.
Good luck, hope thing work out