I think the Prius breaks even against a comparably sized compact car at the 100,000 mile mark assuming $5/gal gasoline. Incidently, the batteries are also shot at about the 100,000 mile mark, so saving money is a real long shot.
I won't be running to get one any time soon.
The tires are also more expensive for the Pious, they have a special size.
They are warranted for 100K miles but that doesn't mean they quit at that point. Priuses used as taxis are approaching 400K miles without needing a replacement.