I know you're looking at some high-dollar cars, but $4k is absurd. You probably negotiated them way down on the price of the car and they're trying to recoup some profit...which is not unethical, but I think you can negotiate down to 2 or 3k depending on the vehicle.
I know someone who got a warranty for an '08 CLS550, AMG appearance package and 59k miles. It cost her somewhere in the neighborhood of 3000-3500 but only because she was a massive headache customer who we honestly didn't care if we ever saw her again, she wasted so many people's time. She came in a week later to yell at my manager because the inside of the cupholders were scratched (EL OH EL), and to put the car on a lift to address other issues Germain MB wanted $150.