From Performance gearing....
"Doug,
A complete final drive with 4.10 gearing and limited slip, ready to bolt-in to your Z4 without any modifications would be $2450.
Shipping within the US would be $75.
If you are not in the US, please forward your postal code and I will forward an exact shipping cost.
thanks for your inquiry,
Jim"
Damn good price and quite tempting with a three year warranty unlimted mileage.
http://www.performancegearing.com/