I suspect that you meant "aluminum body" and not "aluminum chassis". Original Cobras have a "steel tube chassis" with an "aluminum body".
However if you really want an "aluminum chassis" and custom built to your specifications, then Kirkham will do that for you.
They charged Larry Ellison at least 1 million dollars to build his car with an aluminum billet chassis.
There was an article in the September 2011 issue of Hot Rod magazine that stated: "The price tag for the research and development of the original billet car was north of $1 million. Now that the hard work is done and the CNC programs have been written, KMS says it can reproduce the car for between $300,000 and $400,000."
Here is a link to that article:
KMS Copper And Silver Cars - The Goddesses - Hot Rod Magazine
Here is a link to the book on designing that car:
Kirkham Motorsports - Leading manufacturer of aluminum bodied 427 and 289 replicas
Here is a link to a discussion of the car on this forum:
Million Dollar Skunksworks Kirkham
Here is a link to another article:
Kirkham Motorsports Billet Cobra Frame
However, like I said, I suspect you want an "aluminum body" and not an "aluminum chassis", so the pricing for that at Kirkham starts at $80,000 without an engine and transmission. A complete car will be at least $100,000.
Here is a link to pricing and options:
Kirkham 427 KMS/SC