Those LiIon prices are for low volume, highly specialised markets. Mass produced lithium-ion is in a different league entirely.

The latest 18650 size LiIon cells (roughly AA sized) cost about $2.50 each when purchased in high volumes. (I think that's still quite a bit more expensive than they could be in the future, when you consider that another very mature battery technology, Zinc chloride, costs only about $0.25 for the same size cell.)

Each 18650 cell weighs about 45 grammes and the market leaders contain >200 Wh/kg. This means each cell can store 9 watt-hours.

As each costs $2.50 to purchase, the current cost per kWh is about $280 per kWh (though you need to buy a lot to get this price). Larger cells and mass production could see this price fall quickly.

A plug-in hybrid doesn't need a huge pack, and can make do with, maybe, 9 kWh of storage (the same amount as in the EnergyCS plugin Prius - and enough for about 40 miles per day EV range before the engine kicks in). The battery cost would then be only about $2,500.

Considering that's not a lot more than the ~$1,000 Toyota says the existing Prius NiMH pack costs, I think a fair number of people would be prepared to pay a $1,500 premium over a base model Prius to enjoy, as you say, 100 miles per dollar motoring for the first 40 miles of the day.

http://mysite.wanadoo-members.co.uk/ecotech/ecot.htm