both rear brakes, including calipers and e-brake cables that are rusted and frozen, need replacing.

Get another quote. Someone is tryin to take ya for a ride.

That is way to high. l do stuff like that almost every day and it should not be more than a couple hundred bucks.

Normally I'd say yes, but it sounds like you need a lot done. You might find a place that will be lower, but probably not by much. l had my brakes done on my Sable not that long ago and it cost a couple hundred bucks just for the front ones.

to replace the rear brakes and the calipers and cables. they are probably flushing the system as well. that is not a bad price. most of it is parts. now that is if the dealer is doing it. if at an after market shop then they are charging too much for parts. ask for a written estimite and post it here then we can have a better idea of the cost.

Calipers? Your Sable must have discs in the rear. In that case, the quoted price is not unreasonable.