Well, I've been in the car business since 1986, and in management since 1988.
And, about an hour ago, my sister called me from a Toyota dealership in Chicago (1200 miles away) with almost the exact same story; the Prius they've waited a year for is here, but the price is $420 higher. Their buyers order says "'05" on it, though. The manager told her that the salesman mistakenly priced it up as an '04.
And, they are trying to steal her trade, offering her $1500 less than it's worth (it NADA wholesales at $18000, but in the real world it's worth $16500, and they're offering her $15000).
I advised her that a signed contract is exactly that, but the mistake could be real and that she might want the car enough to accept it. And that the dealership is going to deliver that car to her or to someone else, it doesn't matter to them. And if they don't offer her $16500 for the trade, she can always retail it for $18000.
So, does she want the car bad enough to take a $420 screwing? I'd walk, but another guy might not.
Priuses are false economy anyhow; you can never make up in fuel savings what you paid extra in up front costs. She should buy something else, a Subaru Legacy or something like that.
Tom