^to help with the haggling, here's a couple of links to the msrp of the rear disk brakes and a spare key.
http://www.realoem.com/bmw/showparts...24&hg=34&fg=10
http://www.realoem.com/bmw/showparts...75&hg=41&fg=50
do note that the key itself does not cost $600+, it should be about $150 worth.