Ok, let's back up. I know it's a stealership but scheduled maintenance sounds like warranty to me. They hide all kinds of cost, including the "service" advisors rates when it is warranty maintenance. If you aren't paying, it is negotiated costs with BMW NA and is good for a laugh when you get the ticket back.
All non warranty work is negotiable and you deserve to be robbed if you take their first three "estimates" seriously as the advisor is commissioned on the margin he can take from you.
If you can't do it yourself or get the parts at the dealer, find an indie shop that can do it a lot cheaper. Mine would change a valve cover gasket for me at their parts cost and a six pack.