Farecast screencap for ORD-DCA, roundtrip flight leaving the day before inauguration (1/20/09) and returning the day after, taken a few minutes ago:
Don’t freak out too much, I found cheaper fares on Kayak. If you want tix, better contact your Representative or Senator soon. My guess is that the latter is a better bet.
Update: Oops! Those cheaper fares were Milwaukee to Harrisburg, PA or Albemarle, VA, both over two hours away; for a bit more money, you can fly from O’Hare. Chicago proper to DC proper is expensive as hell. Sorry about that.
Update II: Actually, it’s probably cheaper to fly into Philly or somewhere north and take the Acela; you could do that for under $300 right now.