I do not won a Metris yet, but my research has been intrigued by this thread.
I can't help but wonder why the part for this fix is a $1000 alone...
So, I am wondering if the parts are similar other Mercedes parts. If you look at the picture in Post #44, it seems there are two purge valves, the oil separator, hoses, and a new elbow for the air intake. Is the new air intake elbow necessary? It looks like a newer design.
Since the Metris has an engine platform similar to other Mercedes (as mentioned in another post above), I would be inclined to think one could use the purge valves and the oil separator from a more ecumenical part, ie C300 etc.. This is one I found in my google search :
O.E.M. Crankcase Breather Intake Line Assembly Call (310)626-8765. May Qualify For FREE SHIPPING. Parts# 274 090 17 29 274-090-17-29 274.090.17.29 2740901729. SLK300, SLC300, GLC350e, GLC300, E300, C350e, C300.
www.pelicanparts.com
Assuming your hoses are still good and the old air intake elbow is still good (not sure about the design change seen in post #44)... I am wondering if a parts swap would be a favorable path. It seems the Metris version is just different hoses. So, just use the purges valves and the oil separator from the cheaper assembly and use your old hoses.
I am not a mechanic nor do I play one on TV, I'm just cheap!