In addition to the price increase that's been announced, the destination charge is also increasing from $540 to $580. See the following link: http://www.autoweek.com/news.cms?newsId=103536
Or, possibly, the price of the fuel used to deliver the cars to the dealers has increased so someone is looking to break even. Even if Prius Drivers don't see the full economic impact of Fuel price increases at the pump, the rest of the economy does, and we still get to pay for it.