I know you can stay at a much cheaper hotel or motel outside of the city. Try to find something in Baltimore County or Ellicott City or even Glen Burnie. I'm sure you will find something dirt cheap but you will have to drive to the school in the morning but it's not hard and there is no traffic before the time you have to get to the school.
For the interview itself, go over what you wrote for your strengths and weaknesses in your essay or something (I thought I blew this one but I got in, anyways). Go over SDN interview feedbacks and you should be set.
Good luck and hopefully I'll see you there in Fall 2005.