i'm going to high-ball it with a guess just short of 1/2 million, say 475k!
Personally, i think the volt and other vehicles like it (series hybrids) are just what transportation needs now... pure electric for short (common) trips and the ability to extend range using gasoline (or whatever generator fuel the future brings). If the bidders on the first volt agree with how significant an advancement this is, i can easily see the bids going higher. 'twould help if the car was actually already in showrooms though...