A lot of money new. It´s hard to find a used one. After I bougth mine, I saw a 1986 4 door G300 that had a MB 300TD engine, that I assumed it was installed by the owner, and they were asking $ 7,500 (US).
I had luck with mine, since I traded an ´83 bmw 525e plus $ 1,300 for it.
Regards