In 2010 I bought three different times three lenses from Arsenal Photo through the famous auction site and "Best Offer", all new with factory warranty; the C-Sonnar 50- $900, C-Biogon 35 -$680 and Biogon 25 -$900 ; delivered to the States. The lowest price I could find including B&H and Adorama then, excellent service with prompt delivery via $40 shipping cost UPS registered.
If you are located in Europe then to purchase from a EU company could be more convenient (VAT). You can also try shphoto-gmbh
in the same auction site as they were selling Zeiss gear since years.
BTW, Zeiss RF lenses are in short supply since months, so keep an eye on the classifieds here too..