First off, keep in mind the hybrids aren't that much better for typical daily use. The Prius gets around low 40 MPG on the highway. It really only makes a difference if you typically city drive, where you can get maybe 50 if you're lucky.
But the hybrid does this by running on battery and shutting the engine off. If you have a stereo system you're going to cause the engine to run more and there goes your MPG benefit. How much? I don't know. But it's definitely something to consider.
And you can get some straight gas vehicles that can do 35 on the highway (Corolla is the only one I know of the top of my head. My '07 manual gets 36MPG from my daily use, which is mainly highway at 70MPH). And it costs at least $6000 less than the Prius. Are you really going to save that much in gas over the life of the cars? Hard to tell. And how much will it cost when you have to replace all those batteries and how long do they last?
I wonder how a Prius would run on a bank of Kinetiks //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif