Priuses (Prei?) are great cars for the efficiency but hardly worth it for most people until gas hits $8 or better. They use nickel metal hydride batteries that eventually decay in output which reduces gas mileage a bit since they use the engine when the battery wears down, but they do not require battery replacement for the duration of the normal car. NiMH is the same type of rechargeable you have in your camera.

The way to get a Prius is to schedule one as an eventual replacement for your present ride when it wears out, gets wrecked, stolen or goes back to the leasing agency and hopefully not all the same day. This is because there is an average two month waiting list on Priyuses plus the buy-in cost is not justified over what you may have now. You also may want to wait for the Prius-smasher supposedly coming from Honda next year, because they claim the difference between their hybrid and gas-only version of the same thing will be limited to $2k.