Diesels are more expensive to build and maintain for a few reasons: Obviously they're not real common here in the USA. They are more heavily built to withstand the high compression and turbocharging, and because they're often used in industrial/commercial applications. Turbos and charge air coolers are expensive. Diesel fuel systems are more complex and precise than gasoline fuel systems, and the injectors have to work with the tips in the combustion chambers. Fuel filters become more expensive and more important as the systems become more complex.
Gasoline engines are catching up in terms of fuel system complexity. These direct injection systems are essentially the same as a diesel common rail system, though the fuel pressures are lower and the combustion chamber temperatures and pressures are lower. I'm sure Ecoboosts are fine engines, but I have some reservations about repair costs. That high pressure fuel pump and those injectors could be expensive, and no doubt those turbos are expensive. I also have doubts about a turbo's longevity in a typical automotive duty cycle. Most of the wear on a turbo occurs when you shut the engine off, and the turbo spins down with no oil pressure provided to the bearings. If a car makes a lot of short trips, and the driver shuts the car down without idling for a bit first, the turbo bearings will wear a lot faster.
I don't think diesel cars make sense in the USA from an financial standpoint. They cost too much, the fuel costs too much, and the maintenance costs too much. Automotive diesels might last longer than gasoline engines, I'm not sure, but either one will last long enough nowadays for the car to fall apart around it. My brother's 1994 Corsica was a good example. It ran great, but the car was falling apart. How many people will keep the car that long anyway?
1997 Oldsmobile Cutlass Supreme SL. 3100 v-6. Auto. 4-door. Green.
2004 Chevrolet Silverado. 5.3 v-8. Auto. 4wd. Long bed. White.