How Much for Part and labor to change Driver's side seat belt

I don't think I could estimate that job because I don't have a labor guide for that car. The labor hours time you estimate is a standard time in a book. You could call a BMW dealer parts dept to find out how much the belt will cost there first, knowing that price is important because that's your "list" price. The "book" labor will depend on how much trim work is involved and how the belt is attached. You can ask for "the book time" and the "list price" when you're getting an estimate. If you want to find a specialist, here's a directory link for you: https://repairpal.com/bmw-repair-in-santa-monica-california