if you want to have it really cheap, and do not mind about the maker.
From Germany. That even beats the FCGroton price.

3 years guarantee.

But look at the evaluation of the seller.

Power seller with almost 72.000 sales transactions, and 99.9% positiv.

http://cgi.ebay.de/QUERLENKER-KOMPLE...ayphotohosting

4 brake discs for E34, 99 EURO buy now
http://cgi.ebay.de/4-Bremsscheiben-B...QQcmdZViewItem

95 more pages of offers
http://stores.ebay.de/Autoteile-Onli...QQftidZ1QQtZkm

Well, tempting, but I think I stay with the brand names.