I couldn't agree with you more. Besides all that they are trying to rape me on the cost of replacement. $2,500 is just plain silly.
Either way, I would try to negotiate and ask for 30%. If you have to pay, you might as well have them help you as much as possible. I know it's not the 50% you wanted, but 30% would be a lot better than nothing (and certainly better than 20%).
Or, you could go aftermarket, but I've been a stickler for OEM stuff so I always suggest it first.