You can "extend" for a year, I think... just not at the same rates / interest etc as your current deal. 6 months with an order number is the longest I have heard of, but I have (admittedly) not heard of everything.How are you planning on extending the lease for one year? That isn't an option that I have ever heard of. I have heard of a couple of months extension to cover production time when you're buying a new vehicle.
To answer the question, it would depend on the required services, but assuming you are at 36k miles at lease end and would need the 45k during the next year, it doesn't seem to include anything major, so I would estimate a couple of hundred bucks, give or take.