Fees at Dulles (KIAD)?

I am going to take an instrument training seminar near Dulles in
January and am trying to decide if I should fly down (1.3 hrs) or
drive (3.5 hrs).

Flying sounds a lot more logical but I am wondering about the fees
charged by either of the big-time FBOs there. I think it is Signature
and Piedmont/Hawthorne. Folks driving Gulfstreams and Beechjets
probably don't think about those kinds of things and they probably
make up most of the customer base. I'm flailing along in a Beech 23
and really cannot afford to have the charges add up to the value of my
airframe!

Has anybody done an overnight at KIAD recently? What kind of chrages
(and reception) did you get?

Thanks,

Jack
Sundowner - N6363U