So I've had 2 diesels in my somewhat limited lifetime. Our current one is a 2012 VW Jetta SportWagen TDI. Great car, haven't had any engine problems and am already working on 120,000 miles. We drive ~130 miles a day just to work and back.
The other (and best) was our 2006 Jetta TDI. The one without the urea injection. Could consistently pull 48 MPG out of her. Amazing car and I kick myself all the time for wrecking it. We'd probably be at 300,000 on her right now with just regular maintenance.
Both of these were maintained by VW service as we always get the extended warranty and like to make sure there's no reason they could deny a claim.
Want to know how much more it cost me to service her over say the 2.5 gasser? Absolutely nothing! Service costs are the same for either motor, there's no diesel specific pricing.
With that said I've never had anything diesel specific go out that would add to the costs over a gasser, but I do know someone (my landscaper) who ditched their 6.7 powerstroke for the V10 because he kept having diesel specific issues that became quite costly. That and on a truck it is a ~$9000 option...
Coming from the other end of the spectrum, I currently have a 2008 Chevy 2500HD with the 6.0 gasser pulling my ~9000lb WA2715 (when fully loaded) and I sure do wish I had the duramax allison combo... I bet the extra torque and mileage would surely make up for the initial cost difference in the end.