Where can i find really cheap flights?

I need to find cheap flights soon. The departing location would be Dulles International next to Washington D.C. and the arrival location would be Austin Texas. I looked on a lot of websites but the cheapest one is $300. My friend moved there a few days ago and he said he only payd $200 but i cannot get hold of him to ask him how he got his so cheap.Where can i find really cheap flights?
It depends on when you are going. Maybe your friend flew when fewer travelers were on board. If you fly out of Baltimore, you can try Southwest Airlines. United has a lot of flights out of Dulles so you can try them. You can also visit sites such as http://www.kayak.com. Keep looking as airfare prices are always changing.Where can i find really cheap flights?
flyertalk.com it's got great deals.