Reading through some of the posts moves me to revisit the budget question. I could write a long post breaking down the costs, but all I'll say to the OP is: Make your theoretical reservations for accommodations, travel, etc. Throw in $50/day for food and another daily amount for admission charges to the attractions you plan to see (not every place is free-admission Washington, DC), and then please report back on your projected budget. I'd be interested to see what it is.

BTW, when you see or hear about those "bargain" hotel rates in major cities, don't forget to add the typical +/-%15 tax most cities levy on a hotel room. The $200/day room then becomes $230/day.