They are $1700 + shipping if you can get one. They are hard to come by.
You need to have the pre- march '07 build, non-welded differential. IMO this is the single most important performance mod for the 335. I want to get as close to my original purchase price -- which I think Autotech will try to keep the price at when they are able to get more. If you get them direct from Birds yourself they are a lot more because of shipping and taxes.