As things currently stand, gasoline hybrid electric vehicles ("HEV" as opposed ot plug-in hybrid vehicles, or "PHEV") cost approximately $3,000 more than an similarly equipped gasoline vehicle, although the actual hardware cost may actually be more.
However, a gasoline direct injection (GDI) engine, with turbocharging, such as GM's Ecotec (Chevrolet Cobalt SS) or Ford's Ecoboost (Taurus SHO) costs only about $750 more than its naturally aspirated counterpart.
When you down-size from a power equivalent naturally aspirated engine, you gain about 20% in fuel economy by going to turbo direct injection. The hybrid fuel economy improvement is typically around 40-50% EPA combined.
As GDI type engines become more common, consumers will have to choose between a system that offers half of the fuel economy benefit for one quarter the cost. If gasoline continues to be affordable (say, sub-$4.00), and Congress doesn't enact large tax incentives for HEVs, I don't see large scale adoption of HEVs until their costs come down dramatically.
I know that I, for one, would choose GDI over HEV in the current market. GDI doesn't force you to sacrifice cargo space because of batteries, and doesn't make the car heavier. It doesn't give you the strange feel of regenerative braking. And it gives you lots of fun-to-drive torque very quickly.
