I too have noticed the prices of these plummet over in WA.
There are heaps of E53 's for sale.

I like Smokey have a well maintained Diesel E53, would hate be selling it at the moment .
The price is not unreasonable at all considering the car that you get.
look at a 100 series turbo , not even in the same league but fetching nearly 40k still.
Just have to wait for the right buyer.