I bet it takes a while to organize a load and I bet the price changes with where they have to go to pick them all up and drop them all off. You could buy 8 at Meecum and haul them all to one place and it would be quite reasonable.
Bingo. The contracts often state as much. The only valid bid is the one on the day of pickup. If you can fill a trailer (myself and a buddy did it when we moved 5 years ago, 3 cars, 2 bikes in an enclosed trailer) the price drops considerably. Same trip back then would have been $1800 per car, but in the end it was more like $950 ea, or about $4800 for all 5 (because it was a single load single drop.