vhtran, if that GS rattles already in the short test drive, walk away from it. You do not want to deal with having the dealer take your whole dash board apart, trust me.
If look hard enough, you can find a 3 to 4 year old 5 series for mid $30K, but then why would you want a 4 year old BMW that may come with a repair bill already. I own a 08 Audi A6 and I can tell you that it is not as fast as the GS, but it handles better. If you can afford a 09 A6, that would be ideal, since the 09 have the new supercharged engine.