I had mine done, (07 328). Cover is plastic, I believe?...Dealer did the repair, an oil change and a couple of other things just before I bought the car. Dont know how much it would have cost because he did the work on good faith, as they found it actually when doing an oil change at my request.
Its not hard to do at all...if your mechanically inclined. A DIY on this job is a good idea....if you have a good indy, thats great....but a valve cover job an any car should not exceed 200.00....just saying.
watch for your power steering reservoir to weep fluid over time. also as mentioned above, the oil filter seal is suspect too....