1999 BMW 740 Timing Chain

Apparently the timing chain guide(?) has broken into pieces that have gone down into my oil pan and the only mechanic I have ssen to this point does not want to do the work due to the nature of the problem. Before I go looking for other mechanics what do you think the cost of these repairs would be. The engine still runs (I have not driven it since I found the problem) but the pieces get into the oil pan and make a noise, the mechanic did not think the pieces had gotten into the engine itself. thank you