Performance Products had a 15%-off sale recently - $552 for the pair of them shipped to my door. Quite lucky to at least get them on sale. And it turned out to be a good idea to get both sides, because the non-leaking side looked like it was about to leak.
Rather a strange feeling to have the axles represent a significant portion of the car's cost - but it's good to go in this department....
If/when I change cars (should the garage-kept granny-driven 300D with 50,000 miles show itself) I'd seriously consider swapping the axles before getting rid of this one.