Discount BMW Parts
These guys have Bosch 12-13-8-647-689 for 31.10 each. But.... it is only for build dates from 10/2002 forward. I see you have an 03, but you will need to check the steel sticker in your door to confirm when it was built to see can use these. You will be just under 190.00 shipped to your door if your build date is not to early.
Depending on if you need the spark plug connector or not you can get them as low as 40.38 each if you have an earlier build date. I wouldn't pay autozone prices unless you might need to take them back or something.