From Wikipedia.
There were 6 cars built for the film, 1 was a fully road worthy which is now owned as noted by Peter Jackson. This car was privately owned by Pierre Picton of Stratford-upon-Avon from the early 1970s until May 2011.
The 5 others were a smaller road going car, the hover-car, the flying car, a transforming car, and a motorless cassis for trailer work. The smaller driving version is in the Dezer Car Museum in Orlando, Florida. The Hover car was mounted on a speedboat and was destroyed after filming. The others did have engines added to later promote the film. The final road version is privately owned by Anthony Bamford, and is on display at the National Motor Museum in Beaulieu, UK.
There are 7 replica cars as well.