In Germany they ask about 1.6 Euro for one liter 95. Or 9.4 $ per gallon.
That's roughly 100,- Euro to fill up a car - and it lasts me little more than 300km in case of my Challenger.
Diesel is cheaper than gas in some regions and more expensive in others, which makes comparing prices a pain in the ass.
I fill up in Switzerland whenever possible. That usually saves me 15-20 Euro.