I ran some rough numbers at work and it showed that over a length of time a prius is still a cheaper car to own... Emphasis on real rough.
I assumed 5 years of ownership(average person), 20k miles a year, $4 a gallon gas. I also assumed that a prius costs $20k and a Volt costs $40k. I'm ignoring depreciation and maint. Assuming you finance both vehicles 100% @ 0% interest... Payment on $20k prius is $333 and the volt is $666. Yes i said it was rough..
100,000 miles over 5 years costs ~$1700-1800 in a volt @230mpg
100,000 miles over 5 years costs ~$8000 in a prius @ 50mpg.
There is a $6200 a years savings over 5 years to drive a volt. However at the same time you've paid double the payment and double the money for the car. So assuming you save $333 a month in payments and deposit that money, the difference in the monthly payments of the two cars, into an ING account returning 1.5% You get a future value of that cash flow of $20760 or so.. So you make $760 by just investing the money in a crappy bank account @ a crappy interest rate. Get a better interest rate and you'll make more $$$$..
If you don't want to mess with saving the difference. Think about the straight costs. You are saving $20k in vehicle price. Subtract the $6200 a volt saves over a prius in fuel price and the volt is still $13800 more expensive. Assuming all the assumptions stay the same(equal maint $, etc), over 10 years the Volt would save you $12,400 over the prius, but that still means the prius is $7600 cheaper....
So what does this all prove. Despite the great numbers from GM, the car needs to be cheaper or energy costs need to be much much higher, to make these vehicle a viable option for the average American..
Please pick apart my numbers. I may have made a mistake.