My "Check Break Linings" light just came on. How long do I have to replace the pads? I saw a post that it would cost $1K for all four at the dealer. Is that accurate?

Also, about a week before the light came on, I started hearing a strange, almost electronic sound when I turn. The sound seems to come from the front left wheel and is worst when the X is cold. Is this related to the break linings, or might it be a different problem?

TIA