The good folks with the Prius Team have shared some details in the PriusChat forums about the Prius I and a "price adjustment" on the Prius II-V models. The Prius I is the "base" model Prius that was announced to compete with the Honda Insight on price, while still offering the MPG and size of the Prius. Between January to May, Toyota probably was pretty worried about the Insight cramping the Prius' sales figures. So they came up with the idea of the Prius I, a "stripped, not equipped" version of the car.