I just read an interesting news article about the original Batmobile. Apparently, George Barris has always owned it, and it will be auctioned in January by the Barret/Jackson house. This is the car that was used in the show from 1966-68, built by Barris. The article said it's difficult to assess the value of this car since it's the original. Apparently it was the 'only' one, and custom cars such as this are extremely rare to go to auction, so there isn't anything to compare it to for a price. The car was the original 1955 Lincoln Futura and converted into the Batmobile.
Here are a couple of links that allow you to understand the full story of the Batmobile.
I think everybody knows about this great site:
Here is the Futura through the years including some nice ones in the middle of the page of it at Barris Kustom before being turned into the Batmobile:
Also a bunch of stuff on the other Batmobiles:
Here is the Barrett/Jackson press release:
Look for the auction on January 19th sometime between 5 and 9 p.m.!