They are Used lenses prices and the 17-40 they got is mint condition.
Prices over here are really hight
and I thought we were getting screwed on the mainland EU. You can buy the 17-40 and 24-105 for US$850 and $1040 new here in Holland.
Plenty people buy a kit (5d2/5d3) and sell their 24-105 immediately, you should be able to find a new lens for less. (I bought mine new at $900)
As for favorite lens, for the first two years the 24-105 was glued to my 5D. It's the perfect one lens travel solution too. Like I said, as your main lens you can't go wrong with it.