I am not sure if Ally requires car to be under warranty, but you can check. They quoted me 4 yrs/48K mi. for my F06 at $4500 and 18 mo. 0% financing. $100 deductible but I spoke with 2 SAs who said Ally is good about claims.
https://www.ally.com/auto/vehicle-pr...contracts.html
I have only had to go once for a failed coil and it was hassle-free at my BMW dealer. They covered the coil (not the plug) and approved it same day.