Volvo's relocated spot for that with the 3rd seat is in the compartment to the left side, half sticks up above floor level. To do it with their parts, you'll need a new bracket with cover. The springs to each side of the unit also need to be switched from horizontal to vertical positions or cds will skip (small square covers cover that).
The bracket hardly looks like $400 worth as it's just a simple one piece bracket. Try calling another Volvo dealer parts department because I think someone's mistaken at that price. I'd never pay that price for that bracket.
If nothing else, I'd just go to a hardware store and find some stuff to make my own bracket long before paying $400 for one. The $60 for the cover doesn't sound bad however and it'll look finished with it, rather than just having it opened and visable.
A potential problem might be that (knowing kids), the temptation to put things inside the changer sitting next to them could become a serious problem for that changer.