Depending on where you are located, there should be enough supply that dealers are discounting. In my case (I live in Metro Detroit), the most I've gotten off for a Prius locally was $500 with a 2 month wait. I wanted to beat the Aug. $300 price increase so I searched outside of the state. The result, $1,000 of MSRP, free delivery from a dealership 700 miles away, and I got my Prius in 4 days.
The resources on priusonline and priuschat are amazing. I'm convinced if I found these sites before I bought I could have easliy saved another $500.
Good luck!