The general public is willing to spend $30k or $40k easily enough. Just look at the quantity of cars on the road that were that expensive when new.
I'm more optimistic about the Volt. It looks like it will offer a lot of value that the Prius doesn't (less funky looking, more aggressive -- looks are very important; size; plug-in and electric-only), in the beginning it will be subsidized, and after a few years its price will lower. I'm not likely to buy a $40k car, but if I could afford it (not right now or anytime in the forseeable future) I'd be happy to buy a $25k car (30mpg V6 2010 Camaro, please). If the Volt can pay for itself on my 80mi/day commute, it could be a strong contender.
Some numbers:
0%, 5-year loan
$25k car: $416/mo
$35k car: $583/mo -- $167 more per month
Miles per month (27 days * 80 miles): 2,160
Gallons@30mpg: 72 ($122 at $1.70, $288 at $4/gal)
Gallons@50mpg: 43 ($73 at $1.70, $172 at $4/gal)
If I never plug it in, the total cost per month is increased by $118/month@1.70/gallon or $51/month@4/gallon.
Now, if I do plug it in...
8kWh per 40 miles of electric-only driving at $0.14/kWh == $1.12 per 40 miles.
If I can't charge at work, that means my morning commute will cost $15.12/month. The afternoon commute will cost $36/mo@1.70/gal or 86/mo@4/gal. Total fuel cost is $50 to $100 per month, halfway paying for itself at $1.70/gal and fully paying for itself at less than $4/gallon.
If I can charge at work and have to pay, that means my
whole commute will cost $30/month.
If I can charge at work and don't have to pay (a distinct reality, I work at a college and the publicity would be worth it to them as well as to large companies where other folks work), my fuel will cost $15/month.
...an then there's subsidized PV for my house, too...