I stopped and talked to some dude sitting in his 2008 Prius. Says he bought the car from Fremont Toyota in about January of this year, 2008, and says they gave him a ... $5,000 'energy discount' off the MSRP. He didn't seem to mean $500 because I said 'you mean they lowered the MSRP to about $21,500 ?? to which he said - yes' I find this hard to believe, but FWIW, anyone else heard of such a thing? search turned up nothing.
after 5 seconds of consideration, and not actually checking what the price of gas was in january 2008 or the average number of prius the dealer had in his inventory, my theory was that this was one of those ads that you see in the newspaper "1 at this price" that dealers run. and that person was just lucky