Good call.. I do everything myself so it didn't even occur to me shop labour. I think Cummins injector swap is 4hrs or so shop time by the book. I'm honestly not entirely sure how long "on average" injectors can last.. OEM vs. ____ brand can have a difference.. but I would say well past 100k and closer to if not exceeding 200k is to be expected.
It's true there are a few things on a diesel engine that are significantly more expensive than a car (comparing individual parts vehicle-to-vehicle), but for cars the options for ultra cheap replacement parts are endless and in comes the old adage of do you buy the right quality part the first time or keep replacing it with multiple much cheaper parts that are of 'disposable' quality. The reason diesel parts are more expensive is (in my opinion) the minimum buy-in for aftermarket parts is of much higher quality on average than the car equivalent.. these engines are meant to be strong reliable workhorses and not just to get the broke college kid's Cavalier back on the road for roadtrip time. On top of that, you have injection pump, injectors, turbo, and maybe waterpump as things that "can" go wrong on a diesel.. but not necessarily need to be replaced after 100k, 200k, 300k or even higher. Of course it's good practice after a certain time period but it's not necessarily required. A car has timing belts every 100k (and the heinous labour costs shop charge to replace), water pump at the same time usually, ignition coils, spark plugs, plug wires, oil every 5,000k, CV joints and boots.. so many things that will likely require attention sooner than a diesel, not to mention more difficulty and time consuming to replace (re: higher labour cost).
I'm obviously biased towards diesels, but I've always been a bit turned off by the "diesel vs gasser maintenance cost" discussions that takes place online, which are usually unfavouring towards the diesel as opined from a gasser enthusiasts.. my somewhat inexperienced opinion is that in the end, like you say about the mileage, the maintenance cost can potentially all be a wash as well.. all depending on brand, how you the user maintains it, how it was maintained before you, how you abuse it, etc.
Sorry Dalko for derailing the thread here.. I just wanted to step in and defend The Diesels' honour!