It's definitely not cheap with 5 people. Camping is $20 per adult (age 12+) per day and children age 2-11 are $10 per kid per day. Wheeling is extra, but I don't know if it's per person or per vehicle for that.
I've seen the same black 200 Series with white hard shell RTT heading into Tysons Corner at about 7:15 a few times in the last couple weeks. No pictures because I'm heading in the opposite direction driving way too fast.