Engine misfiring on one cylinder. Local independent shop says I should replace all eight coils and plugs. Curious if this is a legitimate proposal. $2000 to do everything versus $600 to do just the one coil and one plug that is misfiring. Also, I'm at slightly over 100,000 miles; is there an upcoming maintenance that would require replacing plugs anyway? I'm thinking I'm doomed if I do and doomed if I don't! LOL

Not a good indy, getting the parts cannon as a first resource. $600 for a single plug and coil is also expensive from an indy.
​​​​​​Are the plugs overdue?

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Which engine? Which cylinder? Was the coil or plug actually diagnosed to be bad? Were they swapped around to follow the misfire? Were other factors excluded such as oil in harness, cylinder scoring, injector issues?

Do not replace all parts until you know what the actual bad part is. Fix the bad part and then opt for more maintenance as you wish after knowing the original issue was fixed.

A coil and plug is a twenty minute repair. It should cost much more to do it right. Swapping coils is another twenty minutes. Install of all new coils with proper indexing of plugs is about two hours, diy.

OEM

Ignition coils Left
A2769060501

Ignition coils Right
A2769063700

Spark plugs
A0041598103

you can check

Order new spark plug boot for the coil/plug with the misfire.USE dielectric grease on the both ends of the boot connections. Cheap and simple.. Had this problem with my GTC and the boots were the solution. Cheap and easy but again use the special grease on all connections.

Statistically coils are a low failure item BUT they do come with new boots so by a show replacing them they solve the problem........ for way more $$$.

Example of what I am talking about https://www.autohausaz.com/pn/150523...saAmy_EALw_wcB

I wouldn’t go back to that shop. That’s a ridicules price! What ever happened to “Time and Materials pricing?”

On my 2016 M278 engine plug replacement interval is 50k miles, so I would think yes, you are due for plugs again.

Coils should be good for the life of the car, so if you have one bad one, I'd just replace it. Here's the kind my car uses, note the price, about $45 ... https://www.rockauto.com/en/moreinfo...EyXVJB86hes%3D.

If the problem is the boot, that's even less, about $5 ... https://www.rockauto.com/en/moreinfo...EyXVJB86hes%3D

As somebody said, you have to remove the coils to change the plugs so there shouldn't be any incremental labor time to replace one while they're in there already.