If its the double Vanos, it will be much more costly Id think than single vanos. Im not accustomed to labor rates on European cars, but Id think its around an 8 to 10 hour job by the books. Just like all metal components, the timing chains are subject to wear, especially due to the continual high stress of driving the cams. I don't know what design BMW uses for their chains (link, roller, double roller), but depending on the design, the replacement intervals change. For a standard non-roller chain, Id be inclined to think that the life span would be around 150,000 miles. Double roller is more or less twice that, with single roller some where in between. I found a set of chains, 25.00 a piece (one exhaust and one intake), but you might also need the tensioner and you would need a gasket set, along with fluids. The tensioner runs about $80, gaskets about 20, and another $35 for the oil change and coolant. All told, if you paid $100 an hour for labor, Id guess (could be way off) you would be looking at $1,200 plus tax for the service. Hope this helps,
-Berlinettaa- USMC Motor T